OK, I'm a lurker, but this one is fun and I am avoiding homework.
So there were a few times that we had close calls in the dorms where we had roommates that were supposed to be gone longer, but thanks to locked doors nothing was seen. They obviously knew what we were doing and did some teasing, but...it was college.
The worst time, though, was when I was visiting him at his parents house. We thought everyone was asleep and we were on his futon, "watching a movie" in his room. We were totally in the middle of "the act" (as quietly as possible) when his sister (2 years younger) knocked on the door. Lucky him, all he had to do was zip up. I put my shirt on, threw my pants behind the futon and covered myself up with a blanket. I have no idea what she thought...