Hi guys, this is my first post since joining the board; I had planned to lurk a while before I said hello, but this is something I not only suffered from, I've (almost completely) gotten over it. Sorry it's a longish post, I'm not too good at using few words.
I'm gay and tried for 30 years to deny it. Because I wasn't attracted to women and couldn't admit I was attracted to men, what I mostly felt was flawed, or damaged somehow. That whole time I wasn't "a real man" in my mind, and one of the biggest ways that showed itself was in a public restroom.
Mostly it was "Omigod, I can't start peeing, they will all know there's something wrong with me." It wasn't just the pain of needing to go and being unable, it was the humiliation of showing it. I couldn't even go into a stall because "well, that shows them I can't go too, can't let everyone know." A public restroom was an unsafe place, unless I could find one that was empty. And then there was the fear "what if someone comes IN?!"
My point, and I do have one, is that I finally learned that it is safe after all, there are others who have the same problem, and it doesn't make me any less of a man for taking a long time, or even to stop trying for now and come back. Oddly enough, I always assumed a hung man would never have the same problem. One thing this board has done for me already is dispel a lot of the preconceived notions I had about "huge cock = no body or self-image issues". We all have demons, no one gets off free. The big thing is what we do about it.
So...getting beyond pee-shy: there actually is a concept called "systematic desensitization" used for people with phobias, perhaps you could find some ideas here. Instead of the thing that makes you most uncomfortable, say peeing into a trough with guys all around you pissing like racehorses, you start with the first thing you can do that is just outside your comfort level.
So in this case, that might be going into a stall. When I conquered THAT demon, my life improved dramatically. Do that until it enters your comfort zone, and then you can stretch to the next slightly uncomfortable thing; maybe leaving the stall door open. Or find a public restroom that has really good privacy partitions between urinals and take the one farthest away from anyone else. A bathroom with a lot of background noise disguises whether you're splashing away or not, so if "what if they know" is an issue, you can go or not, no one will know or care. Some bars and restaurants have a lot of background music, and pretty dark restrooms as well, one more thing to add to a feeling privacy in public.
You can see where this is going, can't you? As you take small steps to make the situation that is uncomfortable part of your safety zone, you gradually get to a point where it is all safe. Every success you structure for yourself leads to another success. If I find myself becoming too self-aware or tensing up at a urinal, I repeat in my head "you are safe, this is like being home," which also helps distract the mind from "omigod" (see above).
Now for me, a big part of that journey was coming into my own as an out gay man, and being proud that I am a real man after all. For you, is it ever that you feel you stand out for having a large (or small, for that matter) penis, perhaps not in a way that feels good to you? So much of happiness in life seems to have self-pride and self-acceptance as a foundation--in my pee-shy story, it was a textbook case. The other thing: other guys are really paying a LOT less attention to whether you're pissing or not that it feels like.
Bottom line, I am almost always at a point where a public restroom feels like a safe place now...even to the point that if I can't go, it's just an inconvenience, not a traumatic thing. The trough thing is the last one for me to conquer, but I have faith I will.
I hope I haven't rambled too much. Please feel free to PM me if I can share any more offline.
Don