I was the youngest boy in our class at school, and after gym class we all showered together in this big locker room. I used to get erections quickly when I used the washcloth on the genitals, so I always tried to be quick.
Some of the other kids would notice and laugh, make fun of me. It was pretty bad, I was only 14 and just getting hair down there, late to puberty..
Coach was a big fat guy, and he showered with us, probably not allowed today but this was the 70's.
I began delaying things, most of the kids would get done and leave, often I was by myself. One day in came coach, naked, he had been there with us before but this was the first time it was just him and me.
He was asking me questions and stuff, then I noticed he had a bi hardon, it was huge compared to me. He saw me looking, and told me not to be concerned it would grow when I got older. Then he asked me if I wanted to see how big it got, and began wanking before I could answer. So I did it too, after all, this was coach. Later, I was really ashamed, but it happened several other times. He never did touch me, but still, that bothered me.