"most on juice" - "It’s odd to me they are so narcissistic but yet don’t go fully nude."
If you mean steroids, then excessive use can shrink your balls, so perhaps that's why they will pose shirtless in front of a mirror for s selfie but not walk around nude.
I've often found the fitter the man, the less likely they are to be nude in a changing room. I know there are exceptions, but that's just my experience in the number of changing rooms I've used over the years. Personally, I don't care who sees me naked in a place like that. It's a place where it should be acceptable to be totally nude for a period of time without it being weird or strange.