A nudist beach is great for https://en.wikipedia.org/wiki/Exposure_therapy and something i would really like to try myself to break down the walls of my psychological state of mind.
I too go into men's changing rooms for swimming pools and post-sports showers.
Last time there were six of us in the showers after sports and two others came in when two walked out. I had never been in such a busy shower block before!
All the men knew each other so were all facing each other and talking.
It didn't faze me whatsoever and when you are in a situation like this you can remember it when you go to the gents and use it as a positive memory.