I have another one. Much more shameful. When we were about 14 my best friend and me got chatting to a man in the park, he was about 40 and had a very playful dog, which we threw sticks for etc.
Then this guy said, "do you want to see my party trick?" Ooh yes please! Can't do it here, he said, come to my house, which was nearby. Intrigued, we went along with him. When we got there it was a smart, large townhouse. His family was wealthy and he had never needed to work, but he dabbled in painting in oils and watercolours.
His mum was home and we met her briefly before going upstairs with him to a spacious and sunny art studio with his paintings covering over the walls and half-finished works on easels. He told us to sit on the sofa whilst he went to get the "required equipment", which turned out to be a hard kitchen chair.
He then stripped naked, and sat on the chair. He was excessively thin and very flexible, and he bent his knees double and placed both feet flat on the seat of the chair each side of his naked, bony bum. He then curled his back, stretched his neck down, and proceeded to give himself a B.J. to completion whilst we watched in absolute amazement.
He did not attempt to involve us, touch us, etc.
We left mightily impressed and afterwards whenever we saw him in the park we'd pester him to do it for us again, and now and again he'd say, "Oh, all right then, come along."
One time his mum, who spoke very posh and plummy, even brought up tea and biscuits, then went back downstairs to her own sitting room and hobbies, completely oblivious to what he was really up to.
After we'd seen him do the trick for us a few times suddenly we stopped seeing him in the park, so that was the end of it.
The reason I feel ashamed of this and would never tell anyone in real life is how eager me and my friend were to watch this man do what he did. I guess I feel embarrassed that we were so dirty minded at such a young age.
My friend, by the way, became a nurse.