I caught my brother once. My house has two staircases on either side going upstairs. One set at the end of the living room on the first floor, and one set in the kitchen, which lead up to a room that we would used as our own "teen living room." So one summer night I wake up at 2am to go to the bathroom. I notice the door to the upstairs living room is closed. This is not normal, so I walk over to it and while not locked, it won't open. This is weird. I turn around, go down the the stairs into the downstairs living room, into the kitchen, and up the other set of stairs. The door at the top is closed too, but not locked and not blocked. I open the door. There's two heavy weights in front of the other door. The lights are off, but the TV is on, and there's teh pr0n going on, clearly off some old VHS tape. I can see my brother's head coming out from the couch. He's got a pair of headphones on and a blanket over himself, and his arm is moving up and down underneath. So I sneak up on him and scream "WHAT DO YOU THINK YOU'RE DOING?!?!" and he hits the ceiling!

I laughed my ass off and ran away before he could chase after me.