Kurt always was kind of an asshole, now that you thought about it. He didn't pick up after himself, left everything a mess, and was all around a general slob who didn't really care about his appearance or the appearance of his things.
Thinking back to the disgusting room you saw back at the mansion, an evil thought bubbles up in your mind. If Kurt is such a slob, maybe he'll appreciate these pairs of disgusting briefs.
You take the box to your room, put it in your closet, and grab three or four pairs. You sneak over to the door of Kurt's room, opening it up and peering inside. Just as you thought. Everything is a mess. Clothes on the floor, bed unmade, dust and dirt everywhere. You slip in and leave them on his bed. Laughing to yourself, you're about to leave when you hear the sound of Kurt's keys in lock of the front door. You panic, searching around for a place to hide before your eyes settle on the sliding door of the closet. You slip it open, jump inside, and slip it closed, but leave it open just enough to see out of just as Kurt walks in, dropping his stuff on the floor and yawning.
He notices the briefs lying on the bed. "What the hell are these?" He says aloud, grabbing one and feeling it. He has a disgusted look on his face at first, but it soon envelopes into a small grin. You wince, both at the fact that you really don't want to see your roommate naked and the fact that you don't know what the briefs do. But you watch anyway as Kurt strips down until he's naked. He grins again and fits one leg into the hole of the briefs before putting the other Rin, and rising them up to his waist.
The band of the briefs snap quickly against his waist. "What the hell!" He says out loud, and begins pulling down on them, but to avail. They don't even move an inch. Suddenly, Kurt begins to sway as his body shakes. He lets out a yelp as his body begins swelling outward, arms, legs, chest, and stomach bulging with muscle and bringing the briefs tight against him. He tries one last time to take them off before a grin creeps over his face and he slides a beefy hand down inside and begins pumping hard, as he does, more muscle grows in along with his animal attributes. You can only watch as Kurt turns into a...