I was out shopping with my parents and I had to use the toilets.
It was a smallish mall with only 3 cubicles. At that age I wasn't keen on urinals so I went into a cubicle. The middle one was occupied which annoyed me.
After finishing my piss, I noticed a small peep hole in the stall divider. I noticed the shadow under the stall moving around a lot.
I decided to take a look through the hole and saw a man stroking his cock on the other side.
I couldn't help watching, I was glued. Within about a minute he blew his load, it was the first time I had seen a man cum in real life.
When he finished, I hurriedly got out of the stall. I could see him in the mirror peering over the top of the door as I left. I assume he had been aware of me watching the whole time.
By the time I got back to my parents, they asked me what took so long. I quickly lied that I had an upset stomach while still trying to act normal.