Not full coitus, but when I was 17, my brother opened my bedroom door when i was being fingerbanged (only the second time it had happened). he didn’t see much but enough to know what was going on. he spent the next three years trying to blackmail me with this information and eventually mentioned it to my parents when i slightly upset him at a restaurant… they were totally unbothered. his face when they dismissed it was hilarious.
also obviously done sexy things when in the room with people who were asleep and not been caught. was going to get it on in a room with 3 friends sleeping in it, but then one of them woke up just as we were building up to it so we did not do it