Don't know how often you dudes go to the gym but I go every morning and have seen loads of dudes pop a boner in the showers/steam and sauna. The showers are one long open walk-in stall with like 8 shower heads so when you shower you are standing right next to other dudes.
I've got a hardon many times. Seen most when soaping up your dick it goes from soft to semi and there are times you just can't stop it going all the way to rock hard boner. Dick has a mind of it's own
One experience recently - 4 of us were in the showers talking about this chick that was in the gym, she had the tightest top on with rock solid nipples and her tight little shorts were camel-toe ( that's when the material gets wedged between her pussy lips ) Any horny dude will know, seeing that on a hot chick is an instant boner. ( if you are into chicks )
So we were talking about her and 3 of us were standing there in the shower with rock hard boners, the other dude had a semi on. Always nice to check out the competition
and follow others dudes eyes.
Also, it happens a lot when you are in the steam room or sauna, all that heat and the conversation between dudes near always being about hot chicks, you see dicks rising. More so in the steam room because hardly no one goes in with a towel. And I've not been the only one having a slow jerkoff in the steam room thinking no one else can see what the hand is doing because of the thick steam. Best one is when you walk in on someone who has been alone in the steam room jerking off and you can spot them trying to keep it hidden using both hands.
I've been caught a few times because when someone opens the steam room door the thick steam rushes out and you are full exposed. And also when you have a boner in the steam room but you've been in there for so long and are desperate to get out of the heat, you have to stand up and walk out with a boner to get to your towel or die from dehydration.
Best not be shy about popping a boner in the lockeroom - it happens to all of us.