Not really a sexual advance but what the hell.
It was at a summer camp. I must've been around 15. There was this girl I was really into but I was too shy to ask her out. Near the end there was a dance and I was having an epic internal struggle. Should I ask her to dance with me or not ?
I finally decided I should. After all if she said no the worst thing that could happen was the next few days would be awkward and then I'd probably never see her again. So I started rehearsing how I would ask her out and was really starting to stress out. Suddenly her best friend comes to me and flatly asked me if I was interested in going out with my crush. I could see her in the background looking at how the conversation was going. Naive, nervous and thinking I was busted I simply answered "No, why ?". She then immediately got back to her I saw the smile vanish on her face and they turned around and left the room.
I'm ashamed to admit it took me a while to fully understand what had just happened. tl,dr : I was so afraid my crush would reject me that I rejected her on accident.