Sirius was drunk, drunker than he'd been in a long time, and trying not to think about what he'd seen that night. Maybe he wasn't paying enough attention, maybe, in that moment, he'd forgotten his cardinal rule. The undershirt stays on. But as Kirley banished their clothes he wasn't think about undershirts and the word his mother had carved into his skin. He was just thinking about Kirley and getting some relief and absolutely anything other than Remus and Regulus. It didn't occur to him that Kirley would be the first person to see him completely naked since he'd been disowned.
The feeling of Kirleys teeth on his bottom lip was heady, and he whined low in the back of his throat. The older man always took charge in these encounters, and Sirius was more than willing to be a pliant body. His fingers dug into the skin just above Kirleys ass, hips bucking forward to maximise contact.