Common occurrence in school
 

During the summers, only a few dorm rooms were left open, and they weren't permanently assigned. Anyone there for a few days could use them, just bring your own sheets. There were two to four beds in each room. More than once when alone I was the first to crash in a particular room, but not long after I'd fallen asleep I was awakened by the sound of a couple fucking in the bunk next to mine. There were other times when I was there with a girl and other people walked in on us, usually to fuck but sometimes just to sleep.

I've written elsewhere on this site about some of these experiences.

My wife to be and I got it on in a tent shared with my best friend after hiking and beer. He was sound asleep. She was riding me naked and we thought we were being very quiet... years later he told me he had watched the whole thing even describing her tweaking her own nipples. :-)