We used to live in this really old, small house. You'd walk through the front door into the living room. Go through that and to the right, and you'd go into the kitchen. There was a doorway from the kitchen into my room with an attached closet off the the left, and the back porch to the right. I'm pretty sure my room used to be part of the porch and was closed in a long time before or something.
Immediately to the left of the front door was a doorway into my parents' room, with a doorway from that into the bathroom. That's why I think my room was added later or something - the only way you could get to the bathroom was through my parents' room.
(Yes, you can see where this is going.)
I was young...maybe 1st or 2nd grade. Got up in the middle of the night to pee. Stumbled in the dark, trying to be quiet, through their room to get to the bathroom. I heard my dad making noises, but I didn't know what sex was at that age, and my dad snored like crazy, so in my young mind, it was just that.
Got to the bathroom door, started to open it, when one of my folks said something. I looked over and the light from the clock radio (remember those?) was just enough that I could see the silhouette of my mom in her nightgown, lying there missionary with my old man on top of her.
"What's wrong!?!" one of them exclaimed.
"I have to pee", I said.
I don't remember much more after that, but I do remember stumbling back to my room afterward, still half-asleep, wondering why mom had her legs wrapped around my dad.
Will forever have that image burned into my brain.