Author's Notes: I had no intentions of writing anything like this until that damn AMA, so I'm blaming Alex Hirsch for this and also because I'm suffering from a lot of feelings about these two kiddos and their sibling relationship. Yes, I'm recovering from "Not What He Seems". No, I will not be okay until new episodes start back up.

Disclaimer: Who am I kidding? I can only WISH that I was as clever as Alex Hirsch.

Margarita Monday

Mondays were the worst day of the week until the day Mabel turned twenty-one. There was just something magical about the first day of the week, even if it did mean the end of the weekend and going back to class and all that other junk. (Unless you were Dipper, in which case going to class was actually something to be excited about. That nerd.)

But oh, glorious Mondays, that day of the week – or rather, night – when she could slip into the one Tex-Mex restaurant in town with her friends and sip on margaritas for a dollar. How she'd coveted those of age people with their icy drinks in their bowl-like glasses and fruit wedges on the side. Even worse, she'd been the last of her friends to turn twenty-one, so she'd had to suffer alone while all her friends went out and came back giggling after five dollars worth of alcoholic fun times.

Even worse was the fact that Dipper didn't care at all. Apparently alcohol was bad for the brain or at least thought processes. But this girl was determined. She was going to get her twin brother drunk. In the name of science! After all, seeing how alcohol affected her brother was going to be an experiment for her. He'd probably end up ranting about UFOs to the really hot bartender and potentially ruin any possible romance in her future with him, but really, Dipper needed a break after the end of this semester. He deserved it.

And she deserved margaritas for living with her ridiculously anal-attentive, paranoid, super smart yet also very distracted to the point of forgetting to wash his clothes twin brother. She also deserved to see what he'd be like wasted on so-called girly drinks.

Convincing Dipper to join her was the hardest part, but she put on her best Mabel charm, going so far as to read about some of his more interesting theories with him. She needed him to be comfortable and at ease before springing something like this on him.

About an hour in though, Dipper stopped and gave her a strange look. "You know, it's been a while since you've entertained my conspiracy theories for this long."

Mabel rolled her eyes. "Just because it seems like I'm watching The Bachelor when you're talking does not mean that I'm not watching The Bachelor and listening to you at the same time. Mabel's Guide to Multi-Tasking – check."

"Well, uh, thanks. I guess." Dipper rubbed the back of his neck. "I really do appreciate it. Everyone else just thinks I'm crazy."

"You are," Mabel pointed out with a laugh, "but you're also right most of the time."

Ah, classic – a backhanded compliment, or an insult with a compliment bow on top. Those got Dipper every single time.

"Hm." Dipper glanced down at his notebooks and then at his watch. "You wanna get something to eat?"

Mabel beamed. "I thought you'd never ask, bro. I'm famished! And I know just the place to go."

See, the key to getting Dipper to do things that he didn't want to do was to somehow get him to think that it was his idea to do those things.
Back when they were in high school, he was so insistent that he was the better driver, but they had to share a car, so when she wanted to go out with her friends or on a date, she'd always talk about walking or taking the bus, but he'd get panicky and give her a ride instead. Score. She'd been worried about living on her own or in a dorm at college (and she'd kind of been scared of being split up from Dipper and how that'd affect them), so he'd suggested getting an apartment together. After nights of being on a particularly bad bender when his brain was working overtime, she had to trick him into sleeping, usually by reading her biology or health textbooks out loud, so he remembered how important sleep was to the brain.

And just like that, Dipper willingly went to the Tex-Mex restaurant on Margarita Monday night, fully thinking that it was his idea to go out for food.

"Two margaritas, please, and here's our IDs!" Mabel announced cheerfully as they sat down in a booth on the bar side of the restaurant.

Dipper immediately became hesitant. "Mabel, I don't think–"

"Nonsense!" Mabel interrupted as the bartender examined their IDs, even though he knew her well enough. Gosh, he was handsome. No, she had to focus. Get her brother silly drunk. "The semester is over. We should celebrate! We both got straight A's. We're awesome!"

That didn't seem to convince him well enough. He folded his arms across his chest, looking like he wanted to be anywhere else but here. "I don't like to get drunk."

"One, it's scientifically impossible for you to know that you don't like to get drunk if you've never been drunk before. Theories are just theories until they're proven as facts after multiple experiments are conducted." Mabel smiled, almost more because of the slightly taken aback look on her twin's face. Sure, everyone said that he was the smarter of the two, but she was still bright as a brand new light bulb. "Two, it's just one drink. You can't possibly get drunk off of one drink."

Well, unless you bribed and paid the bartender beforehand for a drink on the double and your brother had a weak tolerance. That might do the trick.

"And three," Mabel continued, "not to peer pressure you or anything, but c'mon, for me? Please? We never do stuff like this together."

"Yeah, well…" Dipper sighed. "Do you…did you want to invite Candy or Grenda or Pacifica?"

As much fun as it would've been to have more people to see the end results of this experiment, Mabel was feeling a bit selfish tonight and slightly nostalgic. "Nah, I just figured we'd have a Mystery Twins Night. We haven't had one in forever."

At this and her softer tone, Dipper relaxed and even smiled a bit. "We have been pretty busy lately."

Mabel blew a raspberry. "School is the worst."

"You mean the best."

"Nerd."

They both laughed. The two of them were definitely an odd pair on campus. The conspiracy nerd brother and the hyperactive cheerful sister. More than a few people had questioned their relation to each other, despite the fact that they looked similar. But Mabel knew deep down that she and Dipper were quite a bit alike. It just ran deeper. No one in this town knew half of the things that they knew.

However, when the margarita was sat down in front of Dipper, he grew quiet again, looking at the drink very similar to the way that he'd look at a shadowy creature in the old Gravity Falls forest. Wary, curious, and a bit confused.

Mabel laughed again and took a sip of her drink, practically propping her chin on the glass. "Don't worry, bro; it's not going to bite you."

"Just in the butt later," Dipper mumbled under his breath. Well, he wasn't entirely wrong about that. He glanced around nervously, as if the patrons of the bar would judge him for drinking like they weren't all three sheets to the wind already. He took a sip with such finality, liked he'd been condemned to a life sentence of drinking margaritas, eyes closed and body tense and everything.

Mabel tried to await his reaction with abated breath, but she was too jittery with excitement and ended up slurping down her entire drink in the process while she watched him. After what seemed like ages, Dipper stopped and sat back up, taking a deep breath. "Well?" she demanded.

"It's…" Dipper his eyes, even more confusion swimming in them. "It's not bad."

"Success!" Mabel cheered. "This calls for another round!"

"You said one drink!"

Mabel stuck out her tongue. "I didn't say for you."

After Dipper's proclamation that the margarita was, in fact, not bad, things lightened up a bit. They were able to chit chat about this and that, something Mabel felt they hadn't been able to do in so long. Both of them were so busy, what with school and social lives and hobbies. She couldn't lie and say that she didn't miss their late night fake sleepovers where they'd camp out in the living room and play video games and read comics and watch super cheesy sci-fi movies and eat junk food. They hadn't done that since their first month at college though before things just sort of changed.

"How much are these anyways?" Dipper randomly asked, pointing to his now empty drink.

Mabel shrugged. "A dollar."

"Oh." Dipper sat there, looking into the glass like it might foretell his future. "I think…I think I'll have one more."

Yes, yes, yes! She didn't even have to make any subtle suggestions. The power of tequila conquered all! She could hear the maniacal laughter in her head. After waving over the bartender, she ordered another round and began to take careful note of everything that Dipper did in the next hour.

Three margaritas later, and Dipper was positively lit in every way. Not only were his eyes shining bright and wide, but he was making wild gestures and talking a thousand miles a minute. Luckily, that was her natural speed and they were twins, so she was able to understand him. For the most part. Every now and then he started doing Science Speak. He didn't even need his notebooks or the Journals to whip out info from them. At one point, he accused his physics professor being a vampire. (She made a mental note to check that out. Oh, childhood dreams.) He was so excited though. Clearly a lot was on his mind these days, but he didn't have a lot of outlets for them besides internet chatrooms and blogs.

Mabel felt a stab of guilt. Maybe she should spend more time just sitting around and talking with him about what was going on in his head, like they did when they were kids.

"One of the psychology professors is talking about doing a class on parapsychology," Dipper exclaimed with such enthusiasm before sipping the rest of his margarita. "Parapsychology! Can you believe it? That would be the best class ever! We have to take it. You have to take it with me. I bet half the things they talk about aren't even correct. They only know the beginnings of Psychokinesis. Remember, Gideon?"

Mabel couldn't stop the involuntary shudder even if she tried. "I try not to."

"He was practically the definition of PSK!" Dipper scratched his head. "Well, more or less. He did have magic amulet to help with his telekinesis. Huh, maybe there's more of those out there."

"Maybe they'll do something on ghost hunting," Mabel added with a giggle. Gosh, that's what she and Dipper needed to do. They should marathon one of those silly ghost hunting TV shows. Dipper liked to say that they were the Real Housewives of the Supernatural, which wasn't exactly wrong, but somehow they both managed to get sucked into them anyways. He'd get all uppity about it and correct the people on the show, like they could hear him, and the lead guy was super attractive for an older guy, but then she'd find herself saying when things were wrong…

Man, their childhood made things funny for them in weird ways.

Dipper shook his head. "I bet they wouldn't even bring up demons."

"Did somebody say 'demons'?" a voice asked cheerily on the other side of their table where a wall divided them from the other side of the restaurant.

Both Mabel and Dipper whipped their heads in that direction and openly gawked at what they saw before them: a yellow triangle with one eye, black lines for legs and arms, wearing a black bow tie and top hat. He was also holding a bright red margarita on the rocks.

"Bill?" Dipper practically shrieked.

"The one and only!" Bill Cipher declared as he carefully leapt over the wall and onto their table, only sloshing his margarita a little.

Mabel took a quick look around the room, but no one else seemed to notice a triangle the color of the sun drinking a margarita except for them. She sat there in a stunned silence, not sure what to say or do. They hadn't seen Bill since… Well, since their last trip to Gravity Falls after they graduated high school. In fact, they had only ever seen him when at Gravity Falls.

Dipper glanced down at his empty glass. "I'm drunk. How many of these did I have?"

"Not enough, kid, let me tell you," Bill replied, taking a sip of his drink. Mabel stared. How in the world had he taken a drink without a mouth? How many margaritas had she had? What did the bartender put in their drinks? "These things are fun in a glass!"

"That's what I've been trying to tell him for months," Mabel found herself saying. She furrowed her brow. "I may have been wrong on that one."

"Ah, don't say that, Shooting Star!" Bill pat Dipper on the head, causing her brother to make a sputtering noise. "You can't let this one suck the fun entirely out of you."

Dipper didn't seem capable of any proper responses at the moment. She could see him beginning to panic. It didn't help that he was drunk. When she'd came up with the idea to get her brother sloshed, she hadn't entertained the thought that a dream demon might show up at the bar to crash their night. Seeing as how this had been her idea though, she had to do something to fix it.

"What are you doing here, Bill?" she asked.

Bill raised his glass. "It's Margarita Monday, is it not?"

"Well…yes."

"Then there's your answer!"

Mabel felt her mouth open and then shut as the cogs of her brain began to work overtime. If what she thought she heard was what he said, then… "So, you like margaritas?"

"Love 'em!"

"Sugar or salt on the rim?"

"Salt, girl, I'm not a heathen."

Mabel harrumphed. "Sugar is delicious. Salt just gets in the way."

"Only if you get something other than a tried and true lime margarita." Bill leaned over and seemingly sniffed her glass. "I'm surprised you didn't get a cotton candy one."

Despite herself, Mabel blushed slightly. Whenever she came here on a night other than Monday, she always got a cotton candy margarita. They were so good though! "So that's it? You just came here for margaritas?"

"Can't a demon enjoy a little bit of relaxation every now and then? Even I need a break from tyranny and nightmares. And Margarita Monday is the perfect night to do that." Bill looked utterly gleeful as he pranced around on their table and drank his drink. In fact, if Mabel didn't know any better, she'd say that Bill was a tad bit…tipsy. "Plus, think of all the poor saps that pass out after this. What fun it is to fiddle with their dreams while in this state! They don't know what's real or dream!"

Mabel smiled slightly. "How about another round? On me?"

"Are you–?" Dipper choked. "Mabel!"

"What? It's a day of celebration! We can't let a little trying to murder us and destroy the world get in the way of Margarita Monday."

"Now that's the spirit, Shooting Star!" Bill finished his drink. "I knew I liked you for a reason. You got a weird head on your shoulders, kid, and that's saying something with a brother like yours."

The bartender dropped off another round of drinks. It seemed as if Dipper couldn't decide on what to do. On one hand, he looked like he never wanted to drink again; on the other, he looked like he needed to drink in order to cope with what was going on. Bill excitedly drank his drink, pointing out exactly what he liked and how he liked it, when to get the best margarita (because, it's not the "where" that matters when you're a demon that can jump through space and time), until he was rambling almost as bad as Dipper had been just moments ago.

"Well, kids, it's been real, but last call is out here and I'm off to the next time zone," Bill announced, setting down his empty glass.

"Don't be a stranger," Mabel told him.

"Or be a stranger," Dipper added. "Forget Christmas cards, birthdays, and all that jazz."

"Oh, I couldn't forget about you, Pine Tree," Bill said, reaching out to tug on Dipper's hat. Dipper nearly slapped Bill's hand away and fixed his hat in an almost protective-like way. "Until next time!"

Mabel grinned and held out a hand. "Next round of margaritas is on you, Bill."

"It's a deal, Shooting Star!" Bill replied with a laugh, shaking her hand.

"Mabel!" Dipper nearly shouted.

And poof, Bill was gone in a blink of the eye.

The two twins sat there for a while, staring at the blank space where the triangle from hell had just occupied. Still, no one in the restaurant seemed to have noticed what had just happened or even that Dipper had just yelled her name. It was like no time had passed, except the empty glasses that marked their time in the booth. Mabel paid for their drinks as Dipper sat in silence. The gears were no doubt whirling around in his head.

It wasn't until they were walking back to their apartment when Dipper spoke up. "Why would you do that, Mabel?"

"Pfft." Mabel flipped her hair back. "I'm a broke college student. Any chance I get to trick a guy into buying me drinks is a win."

"Bill isn't a guy! He's a demon!"

"What's the worst that could happen?" Mabel laughed. "I become Margarita Monday chums with a demon?"

Well, she wasn't wrong.