The shower situation where guys close the curtain vs the open attitude in sauna's and things like that is also something which lives in Europe, at least as far as I now in Belgium. It is strange and I do wonder about it as well.... have no good explanation for it except that it is crazy like hell. You show off, sometimes even display a hard one to other guys with which you played and touched... yet on the point of showering we all get prude.... it is a strange attitude, to say the least, not really now why.
The advice I would like to give to the guy who started this topic ... why cover up when you get a booner? Is not it a psychological reaction which you create? You know that you are going to undress, you know that you can get a hard one? You are afraid that it will happen and indeed ... it is like a vicious circle: for sure it will occure when you are nervous about it and acting to prevent a booner. I lived the same situation when I was a teenager. When undressing or dressing in a locker room with the other guys of my class, I often got a hard one. I felt embarrassed. So I stood there with my towel close at hand, with only seconds to put on my swimming treasure or my underwear.
One day I got so sick and tired of it, I decided to give it up. If I got a hard one, so be it; nothing unnatural. For sure, a got a few ones but luckely for me I saw that other guys, who follewed my example, got one as well. Now, years later, I cannot care less. If I get hard, well I get hard; if people want to look at it, I let them look; if I do not get hard, I do not get hard... I do not care. Why should I? Is not it a normal piece of your body? So why be nervous and ashamed about it? I for sure do not any more....