FUNNY!!! I remember when I was younger (probably 6-9), seeing a teenager at the YMCA in the shower with a boaner, but not knowing why (or even what it was - I just knew it looked different)... When I got a little older, we stopped going and I havn't showered in a public lockerroom since (not even in high school or college - wasn't much into sports). I have thought about if this would happen to me (It has come to my attention that I need to take fitness seriously, and that I should think about frequenting a health club)... I am honestly afraid to go to a gym for that reason.
Honestly, when you think about it, keeping your mind off of what gives you a hardon is what is really going to help you (for example, thinking about Hillary Clinton would definately work... or Janet Reno (eeeghhhh!)). Either that, or just being really used to showering with other guys...