This happened during my fourth year of high school, I grew up in the Toronto area.
After gym class one day all of the guys piled into the change room showers, as usual. We were required to shower after gym class for hygienic reasons. I had a spare the next period so I was able to take my time in the showers, and didn't have to rush to my next class like most of the other guys.
There was another guy, named Dominic, who also had a spare the next period, so we often stayed for a couple extra minutes together in the showers talking about girls, sex, all of the usual things that guys talk about. Dominic was incredibly hot. He was the star of the basketball team and every girl's dream. He had nice muscles, and a firm, toned body all around. He made me so horny that I had to try ridiculously hard to not get a boner when I was naked around him. I usually only saw him soft, but obviously I had seem him hard a few times in the gym showers but nothing sexual ever happened between us before today. His dick didn't really impress me all that much. It wasn't tiny, but not large either. If I had to place it somewhere in the grand scheme of things I would say that it's probably on the small side of average. I never measured it, but it looked like it was around five inches.
I was a bit thinner than him, but also well-toned. I was on the basketball team as well, and was fairly popular. I wasn't quite as attractive as him but that's not to say I was ugly. I was fine looking, I had a girlfriend and all. He was #1 guy and I was his best friend. It was that sort of relationship. My dick was much larger than his, about six and a half inches, which I would often tease him about in private, but for obvious reasons never in public.
Today, when the conversation turned to sex, I noticed Dominic starting to get hard. We were pretty open about sex and such so when I noticed it I pointed it out to him and said something along the lines of, 'gettin 'ya hard? I thought you were only into girls!' Of course this was all joking, I never had any reason to suspect that he was gay. He laughed, told me to shut up and that he hadn't gotten any action in a while.
As our conversation continued I noticed that he was getting harder and harder, and before long he had a full-on boner. From time to time I would notice him reach down and give it a quick yank, he was clearly enjoying the conversation.
I moved to the stall beside his and slapped his butt, asking him if he was horny. He said yes and that he needed some action badly. We chuckled awkwardly and for a moment I let my guard down and started to get hard. Just looking at him made me want to cum. When I realized I was getting hard I just hoped he wouldn't notice.
He did notice, and he made a comment along the lines of, 'wow, nice size you have there!'
We showered in silence for a moment, and then he asked, out of the blue, if I wanted to jerk off. He said that he was really horny because he hadn't had sex in a while and that he really just needed to cum. Of course I said yes, this was about to get really hot!
We started stoking our dicks, at first slowly and then faster and faster. He let out a soft moan and I followed suit. The moans then became louder and louder until we remembered that there was a gym class outside that might be able to hear us. Just then our gym teacher walked in asking what was going on!
We thought that for sure we had been caught, as he walked in we both angled ourselves away and responded, 'nothing, the water just got really hot for a second.'
I'm not sure whether or not he believed us but for whatever reason he left us alone and we were able to continue jerking off. After a couple more minutes Dominic came, and then I came moments later.
After that we got dried off and left the showers, the next day we saw each other in gym class but made no mention of the events.
Later on that year, after he had had a sexual encounter that had clearly ended badly, word got out that he had a small penis. I swear to God that I had nothing to do with it, but he was convinced that I was the one who had spread the rumour. We didn't talk very much after that. Oh well.
It was still super hot, and so was he, and I still jerk off thinking about it.