I don't remember much about the PE showers in my youth (late 70s, early 80s), but for an experience with boys and men naked together, there was one year, one time, at scout camp.
This year was a plain old summer camp (not at a formal camp with day programs, just free-form camping in the mountains).
One of the days, the troop had been hiking around a couple small lakes. Somehow, the suggestion of skinny dipping came up. So, about 2/3rds of the troop (but not me, I was too shy), along with the scoutmaster and assistant, stripped naked and went swimming in the lake.
Nothing unusual back then. Indeed, I bet the cold lake prevented anything embarrassing from ... popping up.