"Alright, ya ready kid?"
"Grunkle Stan, I'm 18 years old, I'm not a kid anymore," Dipper moaned.
"Whatever, kid," Stan replied, throwing his arm around his great-nephew's shoulder. "Think about this, kid; it's prom night! The most important least important day of yer life, right next to the day you file your taxes for the first time, so you gotta make it one worth remembering. Ya got the rubbers I gave ya, right?"
"What? No, Grunkle Stan, Pacifica said she doesn't want to do that!"
"Eh, fair enough, the both of ya are going to Eugene anyways, you can take care of that later!"
"Oh Grunkle Stan, you're so silly!" Mabel said, twirling to get a look at her dress. "I LOOK LIKE CINDERELLA! Kiss me and wake me from my eternal slumber!"
"Hard to believe she's gonna be a Valedictorian, huh?" Grunkle Stan asked. He fixed Dipper's bowtie, licked his finger and ran it through the 18-year-old's hair, which the younger Pines did NOT appreciate.
"Come on, Grunkle Stan!"
"Kid, I'm gonna give you some genuine advice for once," said Grunkle Stan. "Treat this girl right, okay? Even if ya don't marry her–"
"Probably not gonna happen anyway," Soos said without taking his eyes off the TV. "Cuz, you know, she's rich, dude!"
"You're not helping, Soos!"
"Can I finish?" Stan asked. "Even if ya don't marry her, ya wanna make this a good experience for the both of ya. Besides, how am I gonna shmooze it up with the Northwests on your–"
"STAN!"
"Alright, alright!" He nudged Dipper's shoulder, admiring how handsome his great nephew looked and smiled a genuine smile. "Knock 'em dead, kid! But hey! I already know you will!"
"Thanks, Grunkle Stan."
"Better bring that suit back, though," said Grunkle Stan. "Already paid way too much for that."
:-:-:-:-:-:-:-:
Dipper found out pretty quickly that he could deal with the various supernatural goings-on in Gravity Falls easier than taking his kinda-sorta-not-quite-yet-girlfriend to prom. It was really their first official date, and Pacifica–and her father–were not about to agree to let Dipper call himself Pacifica's boyfriend just yet. The kid still had some "tests" he needed to pass in the eyes of the Northwests.
That included the aforementioned escorting Pacifica to prom. Dipper didn't even go last year, he couldn't get a date. Instead, he did something much more fun–tracked down bigfoot.
Though he'd already showered, he was sweating like Grunkle Stan as he knocked on the Northwest's door. Mr. Northwest immediately answered the door, and the glare he gave the young man made him wish he was dealing with Cthulhu and not a prom date. "Hello, young Pines," he said. "My daughter has been expecting you."
"Oh, um, that's great," Dipper said, stopping himself from stuttering. It got worse when Pacifica appeared in the foyer, dressed in a pretty purple dress and her blonde hair in a bun that literally left Dipper speechless.
"Well?" Mr. Northwest asked as if he knew Dipper's plight. "Got anything to say, boy? Or ghost got your tongue?"
"Um, nice… dress," Dipper said.
The simplest of compliments was enough for Pacifica, and she giggled and twirled while Dipper smiled nervously. Really, he was just relieved he managed to avoid Northwest's anger. And he also pretended not to hear Mabel and her date filming the whole thing on their phones in the limo.
After that, he took his pictures with Pacifica before departing for prom.
:-:-:-:-:-:-:-:-:
… Which turned out to be a disaster.
Dipper, by the way, did not catch Bigfoot. He caught Dipper. Yelling something about how he was going to show Dipper what it was like to have someone sneaking up on him and taking unwanted photos, Sasquatch snuck into the hotel ballroom, despite being 7-ish feet tall, and took blurry photos of Dipper dancing with Pacifica.
Once the young supernatural investigator found out, he tried to catch ol' Bigfoot.
About five minutes later, the ballroom was a wreck. No, Dipper did not cause the damage, the 7-foot man-ape did. But Dipper sat on the stage, with his head in his hand, wondering just what went wrong.
That was when Pacifica sat down next to him. "Wow, some prom, huh?"
"Yeeeee-yep," he said. "I never thought Bigfoot had a camera."
"At least you proved he was real," said Pacifica.
"Yeah, thanks," he said. "At least that's something."
"And you looked pretty cool out there," she said. "Especially when you got angry at Bigfoot when he tried to kill me."
"Oh, um, you're welcome," he said with his face turning a bright red flush. "Sorry it didn't go as well as you hoped."
"Well, you did look, like, kinda cool battling Bigfoot," she said. "And it case you were wondering, I'm pretty sure I'm gonna remember this for the rest of my life."
"Oh, um, that's pretty cool, um–I was afraid–"
"Just one more thing," she said, grabbing his messed-up bowtie, "Shut up and kiss me." Which he did. And it was a good kiss, and now there was nothing that could go wrong–
"Dipper and Pacifica, sittin' in a tree! K-I-S-S-I-N-G!"
"MABEL!"