My experiences were always tense and unpleasant. I wasn't embarrased by my body overall, though. It was my dick. It was very big for my age in high school, and got hard at the slightest thought.
In the early-mid 1960s you didn't get a boner in the open gang shower - that was queer. And I was naturally so big I feared the guys might think I was already half-hard. I wished I had a smaller dick, like they all did.
And I sometimes did start to get hard. Couldn't understand why. I was still in denial, never believed I could be a queer homo myself (we didn't say "gay" back then, apparently still an insider term for the homosexual community).
In retrospect I now realize being surrounded by naked guys was sexually arousing to me, but my mind wouldn't formulate that possibility. Not in the closet, just unable to accept the possibility at all, in very deep denial.
So school locker rooms were torture for me. It wasn't much better when I was 20 and had enlisted in the Army. With even less privacy. It helped that I naturally didn't wear my eyeglasses in the gang shower, virtually blind without them. But I KNEW naked guys were all around me.
My trick was to close my eyes as I showered, and think of playing my favorite Mozart piano sonata. I had it memorized, and would concentrate as if the keyboard was under my fingers, mentally performing that calming piece. Sometimes I even hummed it a little. My dick would stay quiet.
Strangely, what finally released me from that problem was coming out, and going to gay bathhouses. There I could get as hard as I wanted in the showers. and everywhere. It was admired, no shame issue.
Afterwards, when I returned to straight locker rooms like at the YMCA, I was no longer troubled by the experience of being naked with other guys. Been there, done that in the proper setting, I could just ignore these other guys. They got no rise out of me.
I found the change in my behavior fascinating. I guess once my craving was satisfied in gay bathhouses, doing all the things I subconciously wanted to do being fulfilled, a straight locker room lost any excitement. And any fear for me. I was totally oblivious to the guys around me, no interest whatsoever. Hence no more unwanted boners.