Luckily I've never been walked in during the act. There's been plenty of close calls. However I kinda walked in my wife's parents doing it one day. This was before we got married and had been dating for a few years. They always told me to just come on in if she wasn't home and hang out. Well one day I come over a little while before she got done with work. I walk in and start going towards her bedroom. As i'm getting closer, I start hearing noises. A few more steps and I hear her mom moaning and her dad grunting.

I hightailed it out of there and went to her sister's house next door. I walked in with a mortified look on my face thinking I was about to get sick. Needless to say I couldn't look at either one of her parents with a straight face nor go over early after that.