In high school my girlfriend's mom walked in on us. The only problem being, she was walking in because her contact had dried out and she needed solution. Being that we were trying to be as quiet as possible, she had no clue we were having sex. Got quite the surprise when she got the contact situation under control. Luckily she was aware that we were horny teenagers and never mentioned it, but I will say it was the most awkward exit from their apartment I ever had.