A/N: This is more or less Wolfstar, because the only two ships I've ever been exposed to for Sirius are Wolfstar and Blackinnon, and the first one is the only one that seems to make any sense in my head even if I'm not a devout shipper.
"Hey, have you seen the…? Oh."
Remus wasn't quite sure what he'd expected to see on walking into the dorm, but this wasn't it.
"Moony?" Sirius spluttered, wobbling precariously on Peter's shoulders and clinging to the canopy of Remus's bed. "I…uh… this isn't what it looks like."
"Really?" Remus replied, closing the door before anyone could come past. "Because it looks like you're using Wormtail as a ladder to get on top of my bed." Peter winced, though it wasn't entirely clear whether that was due to what Remus was saying or the weight of Sirius bearing down on his shoulders.
"Oh. Well. I, uh, guess it is what it looks like, then."
"Can we discuss this once Pads isn't standing on me any more?" Peter wheezed.
"Don't be such a wet blanket," Sirius said, but he did climb off and sit down, while Peter flopped onto his own bed rubbing his shoulders.
"Do I even want to know what you were doing up there?" Remus asked with a sigh.
"Mainly trying to find out if it could hold my weight," Sirius admitted, leaning back with a little grin. Now he'd been caught in the act, he was trying to seem completely unconcerned, as usual.
"And why did you feel the need to find that out?"
"For pranking James," Peter put in with a little grin.
"What was the plan, fall on him?"
Sirius tried and failed to stifle a snicker at the thought. "No, but now you've mentioned it…"
"Oh, shush, you prat." Remus idly lobbed a pillow at him, which was caught and promptly sat on.
"Prat? Excuse me, Moony, but I think you'll find I am not a prat. You're a prat."
"And your comebacks are truly a masterpiece." Peter snorted with laughter and immediately tried to look contrite as Sirius mock-scowled at him. Remus rolled his eyes. "Look, now I don't even want to know what you're going to do to James. I want plausible deniability. But next time I walk in on you two doing something, can it not involve my bed?"
The door creaked open, and James stood there, looking very much like he wasn't sure he wanted to know what was going on.
"…What are you on about?" he ventured.
"Nothing," the three of them chorused guiltily.
"…Right." He gave them a sceptical look. "So… no explanation for what the hell I just heard?"
"These two were trying to do something you probably don't want to know about, and I caught them at it," Remus said, with the most innocently exasperated expression he could muster. "And now I think I'm going to leave them to it because I don't want to see what happens next."
He stalked out of the door, and grinned to himself at Sirius's belated squawk of protest as they all figured out what he'd been implying.
"MOONY!"
He took off down the stairs as fast as he could.