This is a candid vid of a guy sporting wood in a communal shower. (I hope it's cool to post it here.) I'm posting it because it's a chance to sit back and watch the other guys in the shower at the time. No one is teasing, abusing, or in any other way making life difficult for the guy with the boner.
I think it's worth looking at, because it's our own embarrassment we feel when we pop some wood in a situation like that. It's not an issue for other people.
The other guys either haven't noticed; don't care; are ignoring it to reduce any embarrassment for the guy with the erection; or maybe some other reason ... in any event, it's something that guys know could happen to them ... maybe HAS happened to them ... and isn't worth making a big deal about.
My experience was always that I would stiffen up the first time or two in any new public shower situation. Then, after that, i was cool with it. And I got better about just being able to tell myself, "OK, here we go again, it's stiff but that's what we always go through and it'll be better."
Of course, that doesn't mean act inappropriately .... but I don't think you're doing that. And ya sure don't have to have a boner to act inappropriately.