Never seen anyone wear underwear in the shower. While in HS, no one showered at my school. (PE was not very strenuous and sort of a joke). The jocks might have showered after sports, I don’t know.
I college and above, people just showered or didn’t. But NEVER in underwear.
if swimming, some would shower with their bathing suit on. Either the whole time or right up until the end. Then they would take their suit off to rinse it and wash underneath. So, limiting to just a few moments their time nude.
personally, I think folks should do what’s comfortable for them. On the one hand, it’s a shame that men can’t learn and be taught growing up to be comfortable with themselves and each other. I think that was how it was long ago when genders were kept further apart and spaces felt “male” or “female”. When you had to “bath in the river” with the community of other guys or when everyone served in the military and shared hard living, that made more sense. It’s a shame that those aspects are lost now as other things have changed and improved.
On the other hand, there seem to be so many creeps in the world now that it’s understandable that guys are taught extreme modestly. I don’t think it’s ego protection so much as personal fear. If a guy is so concerned with me being naked in the locker room it might just be because he has bad intentions and wants to creep on me. Otherwise, why would he care so much? He’s there for sports and to work out—improve himself. Not to give interested men a show. For young guys in their prime full of testosterone, it isn’t comfortable to be the “object” like that.
That was the vibe for me growing up. And as far as I know, it’s still how guys generally feel today.