Going through school in the late 90s though early 2000s, showering after gym was not mandatory. Locker rooms had showers available, but I never saw them get used. At some point everyone at least peeked and saw they were open rooms with shower heads down two walls. In higher grades, I heard that athletes in football or wrestling used them, but I was far from athletic. That didn't stop me from wondering what it'd be like to be nude with all my classmates.
We began changing into gym apparel in 6th grade, meaning strip to our undergarments and change into shorts and a T-shirt. This was strange at first, being just shy of nude with classmates, but it quickly became normal. Plus, we had the open showers just a few feet away to remind us it could be worse. Even through we still had undergarments on, it was still interesting to see the different bodies and development over the years. But I definitely didn't notice this because there was no way I was anything but 100% straight, right? Though knowing the girls were changing as well on the other side of the wall was an exciting thought, and I'm sure the topic of some self pleasure at the time.
Fast forward to my early 30s... I had been in nude locker room situations less than 10 times, always changing quickly, but not without making a quick, secret peek around. I say secret because I was trying not to admit I was curious. But my wife and I joined the local YMCA, mainly for swimming. Upon entering the men's locker room (18+), I was taken back to the school locker rooms and the open nature. There were 6 or so rows of shoulder high lockers with benches in between. I realized I had no option but to pick the only vacant row and strip nude to put my swim shorts on. After quickly doing so, I headed to the pool, passing through the locker room of men in various states of undress, but not without a few peeks. Last, I had to pass through the tunnel of open showers, with one man showering nude. At this point I felt a bit of a thrill, realizing I couldn't help but wonder what the other men looked like nude and how we matched up. I could no longer act like the glances weren't on purpose. After the swim, I decided to make the full plunge and took my first ever shower in an open locker room. This was yet another thrill, knowing it was my small penis's turn to potentially be the recipient of glances. After wrapping my towel around me, I headed back to my locker, only to realize my row was no longer vacant, with a guy in his mid 20s changing. The final new experience was removing my towel and changing nude, directly next to another nude male doing the same. I couldn't help but look at his penis and notice how much larger he was, feeling a stir when I realized he probably noticed the same.
I've since realized that I enjoy seeing other males nude in the locker room and knowing I can be seen as well. The mental size comparison is enjoyable, though I almost always come out smaller. I can't go to say I'm beyond curious, as I've never after upon the curiosity. Along side that, I find it interesting that the ladies' locker room mirrors the men's, and can't help but fantasize what's going on in there.