I regularly hang out at a local book store, and on most visits spend a little time in the bathroom there, jacking off in one of the 2 cubicles - usually after reading erotic short stories.
On my most recent visit, I entered the cubicle and could hear somebody in the other cubicle. Usually, when this happens I start jacking off, but do it quietly so as not to alarm the other person!
So I started quietly, just gently stroking and waiting for the guy in the next cubicle to leave so that I could get on with it! After about 5 minutes, I noticed that the only sounds coming from the guy next door were short, quiet, quick breaths and started to suspect that he was also jacking off. I started to make just a little more noise, so that it became more obvious what I was doing. He responded similarly and both of us knew what the other was doing!
I looked down and noticed from that guy's shoes that he was now standing-up and facing the wall between us while he was jacking off. This got me real excited... we both started getting noisier. As we went on, we moved towards the cubicle door until we could see each other's cocks through the slight crack between the side wall and front wall. We were both really into it. Now, I'm not gay, but I was tempted to see if the guy was willing to let me in so that we could help each other out (if you know what I mean!). But, I didn't say anything (nor did he) - we just kept jacking off. It wasn't long before I shot my load on the cubicle wall. I quickly cleaned up and got out (but not before I'd taken another peek at the guys cock as he jerked off). He didn't shoot his load before I left, but I went back in 10 minutes later to see if he was still there, I found only the leftover cum on the wall of the cubicle that he'd been in. I never saw the guys face, and he didn't see mine. I do wonder what it'd have been like if we'd have gotten together to finish our little session though... maybe next time!