I'm 22 and I go to a gym that has half open showers. There's a row of showers that have walls between each one, but no curtain so you can see everyone as you walk past.
I quite often get a hard-on when I'm showering. I've tried thinking about other things, masturbating before going to the gym, but nothing seems to work. I do my exercise, take a shower and up it pops. I'm sure other guys have this problem too, but you never see erections in the showers, certainly not in this gym, so it's a bit embarrassing.
Usually if I only have a semi or something I just turn the cold tap on or finish showering and cover up, but today I was rock hard and knew I wouldn't make it back to the lockers without someone seeing. I could hear there was another guy a few showers down, but I didn't think anyone else, so I turned to the wall and gave myself a few tugs and it felt amazing thinking anyone could walk past and see.
I got scared and stopped which was lucky because then another young guy who'd been swimming walked past. He must have seen I was hard, but didn't stop or say anything. So after that I was still harder than ever so I just had to finish off. It probably took me about 20 seconds and I was so excited I couldn't hold back a little moan.
I went back into the locker room and the guy who'd walked past me was still there. Having seen my erection just before he must have known what I'd done, but it didn't seem to bother him. Actually I think it might have turned him on a bit as I saw his cock grow just a bit and then he hurried to put his jeans on forgetting to put his underwear on first!