About 13 years ago I had a really good female friend who was a couple of years older than me. We had sent a few nudes to each other over the years - that was before sexting was really a thing (I guess) - but we were not in love with each other... maybe not even really attracted to each other either actually. Just really good friends, to the point where we could tell each other nearly everything.

One night she visited me for movie night, my parents had already gone to bed and we went to my room to finish the movie. When we turned off the TV and the lights and were about to doze off, she said, that she usually masturbates before sleep. And I let her. The moaning, the wet splashy sounds, and her wiggling body made me insanely hard. For a young man this was close to torture. I recall she said, that I could play with myself too, if I wanted. But. I was stiff-scared (pun not intended). I did not move a muscle. I just stayed on my back, staring into the dark ceiling and listening to her pleasure.

Without doubt one of the most erotic experiences I ever had.