I remember last Fall, during the beginning of the semester, I would be pounding my girlfriend over the side of my bed, and she'd be moaning and 'oo'ing loud enough for the neighbors to hear through the walls, and then my roommate would try to open the door, since he was coming back from class or something. Then we had to jump on the bed, and cover ourselves up (all while still penetrated)
My roommate always seemed to walk in on us.
One time he started asking my girlfriend what she liked in terms of sex, and I didn't like that. And she told him too!
I remember we were having sex on her roommate's futon one time, and her roommate walked on us. She didn't really seem surprised or angry, but she did stare at my ass for a bit
