Fellatio? Oral sex?
Not particularly embarrassing, but I used to ride my horse out onto the football field for highschool home games. At the last home game of the season I was running down the field and turned....my saddle started to slide sideways and off I went. In front of 2 football teams the marching bands and an entire stand full of on lookers.
I only had one teacher mess with me about it.
Inspired by Flink's story, I'll tell a short one I had nothing to do with. My friend was chatting up some girl before a test started, later on he's talking to his friend and the girl comes up and asks what they're talking about, the second guy immediately says Gay Sex....She didn't talk to either of them again.