author's note: This was loosely inspired by Harry Potter and the Methods of Rationality (ID=5782108) by LessWrong. I highly recommend it!

Chapter 1: Sirius Black's Massive Snogfest

James Potter squinted at the parchment Black had handed him. "Bloody hell, how'm I supposed to read this without a magnifying charm?"

Sirius Black scowled. "You don't need to read the damn thing, just cast a Copying Charm or something."

"Right. No, wait, I've got a better idea." Potter unrolled the thirty-inch parchment flat on the Gryffindor common room floor, pulled out his wand, touched it to the parchment, then closed his eyes. He concentrated, biting his lip, and the parchment underwent a Transfiguration. It became cloth, grew to double its size, and all the names did as well.

"Perfect! No, wait, one more thing." Black waved his wand over the banner, and the names rearranged to make room for a slogan: CONGRATULATIONS SIRIUS BLACK / ON A MASSIVE SNOGFEST.

There weren't very many people in the common area, but they all looked up at the floating banner. It attached itself over the fireplace. The boys snorted and grinned, while the girls rolled their eyes. Most of them, anyway; the two sixth-year girls who noted their names on the banner had different reactions. Godiva Turpin shrieked and wailed and ran upstairs to the girls' quarters, while Nessa Finnigan walked right up to Sirius and slapped him in the face. "How dare you!" she whispered then walked out.

Black shrugged while Potter grinned. "Girls, eh?"

"Where's Remus and Peter?" asked Black.

"Still raiding the kitchens I'd assume. I've got a couple cases of butterbeer, will you bring them out? I'm gonna work on the entertainment. "

"You mean that awful noise that resembles cats mating?"

"Hey, a party's not a party without Bowie!"

Black sighed and went up to their rooms to fetch the drinks. He also grabbed his flask – it was too early for firewhiskey but he didn't want to have to go back for it. He couldn't believe Potter. Over the summer he had found out all of Lily Evans' favorite Muggle singers. While he agreed with Black about most of the noise, he was infatuated with David Bowie's music. He'd bought all of his albums and copied most of them into magical crystal form. The crystal played every one of Bowie's songs in random order, and pulsed and flashed to the beat as well. And when Black returned, the crystal was doing so on the mantle, and Lupin and Pettigrew had arrived with the food.

"Excellent, mates." He opened a few butterbeers and passed them to the other Marauders, then offered them to the other Gryffindors. They all gladly accepted. "What's the occasion?" asked Algie Longbottom.

"Black snogged the sixth year," replied Lupin.

Longbottom blinked. "What, the whole year? Every girl?"

"Correct," said Black.

"Except Lily Evans," Potter pointed out.

"True," Black conceded. He would never have done that to a mate. Fortunately Lupin was dating a fifth-year Ravenclaw, Sandra Brocklehurst, so that wasn't an issue. As for Pettigrew, well.

"Well done mate! Cheers!" announced Longbottom, clinking his bottle against the others.

Black settled in on a couch next to Lupin and Potter, and Pettigrew sat at Potter's feet. "I can't believe you managed it, Sirius. I wouldn't even know how to get a girl to agree to kiss me."

"Well, if you happen to be me, you just say, Hullo, I'm Sirius Black. Fancy meeting me behind the greenhouse before Quidditch practice? For you, though, I'd rethink that strategy."

"Yeah I don't think that would work for anyone who wasn't Sirius Black," laughed Potter. "I personally prefer asking a girl to Hogsmeade, and if she lets you hold her hand on the way, suggest the tea shop." Potter had had a few girlfriends, but they seemed to be able to tell that he'd prefer to be with Evans, or at least, not with them.

Speaking of Evans… She walked in just after Potter's advice to Wormtail. She stopped dead when she saw the boys with their butterbeers and the banner hanging high. "Sirius Black, you are a totally disgusting excuse for a human being," she declared after reading the names on the banner. "This is - are you joking? This is every single girl in our year except me!"

Potter stood up. "Black is a rotter, all right. Fancy a butterbeer?"

She shook her head. "There's a Prefects' meeting before curfew, then we have to do rounds. Lupin?"

He sighed and put his drink down. "I'll see you lads later." He followed her out. Potter's eyes followed Evans, and Pettigrew's eyes were on Potter. Black almost didn't notice, but when he did he almost dropped his bottle. Well, he supposed it wasn't so surprising, but -

Potter's voice broke into his thoughts. "Wish you'd lend me some of that mojo you got, Padfoot," he said morosely. "Evans won't even give me the time of day."

"I would, but, getting a bird to snog you is totally different than getting her to shag you."

"I don't want to SHAG her!" Everyone laughed at that, and Potter blushed. "Or – well, not JUST. I – hell, haven't you ever had a crush, Black?"

"Course I have, Prongs. But I think calling it a crush is a bit disingenuous, you've been mooning over Evans since third year."

Potter sighed. "You really think it's pointless?"

"If I thought it was pointless, her name would be on that banner too," he lied. Of course it was pointless, Evans was a wet hen with a stick up her arse. Gorgeous, sure, but so very uptight. Everyone knew she thought the Marauders were all major prats, and she probably wouldn't touch James with a ten-foot pole. But Black would never say something like that to Potter. He couldn't bear to upset him. "Let's get back to the subject of myself and my success, shall we?"

Black started describing what it had been like to kiss Cassandra Brown, the first girl in their year to start wearing a bra (all the way back in First Year). She had T&A for miles, and wasn't at all averse to letting Black get a few feels in. Most of the other girls who hadn't yet left, did during this speech, but one of them, fifth-year Sitar Patil, just smiled and raised her eyebrows at him. He winked at her a couple times.

And then Martin Perks, a seventh-year, walked in. He blanched when he saw the banner, but he quietly scanned the list and was obviously relieved. He grabbed a butterbeer and smiled at Sirius. Sirius smiled back at him. Did he really think I'd be that terrible, to put the names of EVERYONE I snogged up? Black was well aware that most blokes were less than open about that sort of thing. Black personally didn't care who knew he was into guys as well as girls – it was seen as just another crazy thing he did – but he knew he was bigger and better at dueling than anyone who'd try anything because of it.

"Scuse me, got to hit the head," announced Potter. Pettigrew's eyes were still on him as he left.

"Hey Peter, could you come with me for a sec?"

Peter jumped. "Uh, sure, Sirius," he stammered, and followed him back to their room.

"What's up?" he asked.

"You fancy James, don't you."

Putting it point-blank seemed to stun Peter. "What – what – what the hell are you on about?"

"Oh don't act all innocent. Look, if it makes you feel any better, I'd shag him if he leaned that way at all."

Peter blushed. "I don't – don't – what, you're sick, Black. Totally bent, you are. Just 'cos you'd shag anything that moved doesn't mean the rest of us are like it."

He shrugged. "Look, I won't tell him if you don't want me to."

"There's nothing to tell!" he insisted in a high-pitched squeal. "I like girls! GIRLS!"

Protesting too much, noted Black. "Sure, sure you do Wormtail, sorry I brought it up. Let's go back to the party then."

Potter was back by the time they returned. "Where'd you two go off?"

"Oh, come on, you know yer mum likes two blokes at once," drawled Black. Pettigrew's jaw dropped while Potter howled with laughter.