Just one of those things.
I had female domination fantasies since I was a little boy (about age 6 or 7). I also masturbated by this age as well, using a technique that consisted of tucking the head of my penis into my foreskin (I am circumcised, but enough of the foreskin remains to be able to pull it over the head of my penis.), and rolling it around on the mattress of my bed.
I also had a fetish for rubber (I don't know how that came about), and anything that was made of rubber and associated with girls became a fetish object. One of these was girls' sneakers that had rubber soles.
It wasn't until I was about 12 when I learned to jerk off in a more 'traditional' way. But I also worked out a way (using my sister's sneakers) to masturbate using the soles of girl-sneakers.
One day when I was 15, I was visiting my cousin who was the same age. It so happened that she had some of her girlfriends over who were girls who I went to grade school with. The girls were interested in hanging our with each other, and didn't give me the time of day.
Out of boredom, I searched around the house and found a pair of my cousin's sneakers in the basement. I took these to the downstairs bathroom, and started to play with them. All of a sudden, the door opens and there stands Karen, one of my cousin's friends. She shrieks and runs off.
By the time I get out of the bathroom, the three girls are standing there waiting for me. My cousin asked me what I was doing with her shoes. What could I say? I decided to tell the truth.
The girls promised that they wouldn't tell anyone if I would show them what I was doing. So I masturbated for them using my cousin's sneakers as they watched.
This incident has been the basis of my fantasies from this point on. Unfortunately, I was never able to be able to repeat the performance. I was never alone with my cousin ever again even until this day (I see her at family events with her husband,) We never even had an opportunity to talk about it ever again. But she still has that smirk on her face, every time we meet.