There are a few that would fit in this thread, but I'll only add a couple..for now.
- On a public beach at night. There were sand dunes where other couples would go for the same thing. We found a nice clearing, layer out a blanket and had our fun for a while. At one point, I noticed a couple standing nearby taking a peek, but walked off after a couple minutes. When we finally finished and started to walk away, we saw the same couple not more than 20 feet away behind another dune having their fun too. As we asked past, the male half looked up and waved.
- Same beach at night. We'd gone on top of a lifeguard tower and started to play. Since the beach was deserted, we weren't exactly being too quiet. After a while, when we finished, we started to hear a lot of other voices nearby. As we looked up, the beach had at least a hundred other people running around. We didn't know that the grunion were running and it was a popular event. For those that don't know, grunion are small fish that come onto the beach to get laid too. People come and grab them by the bucket full. Yeah..I'm sure we were seen and heard that night too!