When I go home for breaks, I don't really have a good place to stay, but my brother very graciously offers his bed to me for a few days at a time each time I return. My girlfriend is from approximately the same area as me, so she came to my house for Thanksgiving this year. We'd been drinking with my family pretty much all day, and when we were worn out from the pleasantries, we retired to that bed for some action. We were rolling around, making out, progressing. Then, for no reason at all, my grandma walks in the room. She just says, "Oh!" and walks out. My girlfriend and I laugh about it, and my grandma later says, "I'd be concerned if you guys weren't doing that."
A month later, however, my girlfriend is back over during Christmas break, with just her and my immediate family. After another long day, we go back to that room and try again. I'm a little nervous after the grandma thing, so my peen isn't responding as well as I'd hope, but I eventually got it going. But as soon as I broke penetration, that fucking door opens and my brother just says, "God damnit" and leaves. Mind you, my bare ass was in motion and my girlfriend's boobs were out and about. The next time I see my brother, all he can say to us is "sinners."