The apartment was quite horrible, as was to be expected, really. After all, they'd let Sirius choose it on his own, and he'd never been any good with cleaning charms. So Remus spent his first free weekend blasting away empty takeaway containers and stains better left uninvestigated, and Sirius came home in the evening to find the place actually clean, and seemed annoyed by this.
"I'll never be able to find anything!"
Remus frowned at him, and patiently explained, "people always say that, but it's almost never true."
"Except now, when it is!" Sirius looked exasperrated, which was confusing to Remus, because it was an expression he was used to seeing only in the mirror.
"How can it be harder to find anything now, when it's organised, than before, when it was more or less a vague collection of... heaps?"
"But they were specific heaps!" Sirius had his fingers in his hair. "There were one or... two... very specific, heaps!"
Remus simply could not understand this anxiety. "Oh, surely, Sirius, you can just as easily--"
"Look, Moony, you didn't... say... clean up my room, did you?"
Remus was beginning to be seriously annoyed. He'd been getting frustrated over feeling as if he wasn't contributing, as if he were a guest wearing out his welcome, and just when he thought he'd found *something* he could do, because after all, what use was it being compulsive if you couldn't at least put it to good use?
"No," he said, irritably, "I hadn't got to it yet."
"Good!" blurted Sirius, whipping around and running into his room. Remus sat there, still frowning at the space Sirius had recently been occupying, as he listened to Sirius swearing, rifling through the mess of his room, apparently knocking his mattress of the bed, swearing some more, and then wrestling the mattress back into place. Remus was just beginning to move from annoyed to perplexed when Sirius emerged, sweaty and grinning manically, and sidled towards the door with his back away from Remus.
"I'll be back in a bit," he said, and then the door had shut behind him too quickly for Remus to work himself up to proper annoyance. But after a few seconds, with no outlet, his anger exploded out of him in a frustrated "AUGH!" and he threw up his hands and went to sulk into a book. But hours later, and passingly, he could not help but wonder what it had been that Sirius had been hiding behind his back, and why he'd previously been hiding it under his mattress like a thirteen-year-old-girl.
After all, he wasn't an idiot.