Most locker rooms are set up with one big communal shower and maybe a couple of individuals with curtains...and most of the time there is another place for adults to shower.Is there the same concern with 18 year old players showering with the younger players? Maybe all those players are exhibitionists. How is the locker room set up? Is it one big shower or individual showers? Do the individual showers have curtains? If there are curtains and they are not being used, then I could see your point but otherwise, it may be a whole lot of Who Shot John.
I find this a little "off" but not totally off. I suspect that the complaint caused the principal to tell the coach to stop doing it.
Yea, the coach could be nefarious, but its more likely that the coach was trying to be part of the whole team thing, without thinking about perceptions...the younger the coach, the more likely that it was that whole team thing.