This is a really short story but I've read others like this tons of times and I wanted to share my experience.
I was going to see a Broadway play and during intermission I had to use the restrooms. All the urinals were taken up so I went into a stall to urinate. The floor tiles were really shiny and reflective and the stall dividers were kind of far away from the walls. As I was peeing I looked at the reflective tiles, and I could see the guy peeing in the next stall, he had the biggest cock I'd ever seen and I started getting really hard in the stall. He didn't notice but I watched him pee for a while. I then watched the next guy too. Once I got home I jacked off to the memories of it.