When I was in the corporate world, we had a gym that employees could use, and many of us did, including the executives. I was in there one day with a buddy of mine and we saw the CEO of the company getting dressed after his shower while we were changing to start our work out. My buddy made a comment after the CEO (who, by the way, chatted with us quite nicely and seemed like a good guy overall) left about the CEO's endowment, or lack thereof. It was a private joke between my bud and I that both of us were more qualified to be the CEO than he was--referring, of course, to our larger cocks.
It was funny to us, but I can see how I might be hesitant to shower with lower level employees--or with enlisted men if I were a military officer. It sort of changes a balance of power, or at least has the potential to.
On occasion I'll be at the mall or at a restaurant or something and I'll see some guy who goes to the same gym as I do. I can remember thinking on more than one occasion that I've seen the guy naked and wondering if I can remember how my equipment compared to his. Now, admittedly, maybe I'm a bit fixated on the whole "who's is bigger?" thing (after all, I am a member of LPSG), but I have to think that other men pay at least some attention to it. I've certainly seen enough of them checking out my package to support that theory.
One last example...
I now work in academia, and I've actually been in the situation where I wound up in the same shower and/or locker room with students of mine. (I'm a college professor, and students and faculty have membership to the same fitness center, so it's nothing weird or perverted.) I know that such encounters have changed the dynamic between me and those students on occasion. Since I teach in the humanities, a field many of the more athletic or "jock" minded students tend to not consider particularly masculine, I've actually had students begin to treat me with more respect after standing next to me in the shower. Maybe it's that they saw me as more of a real person since I've always just chatted with them nonchalantly when that happened, which is probably part of it. And maybe they had more respect for me since I was there working out, which also levels the playing field some. But I also have to believe that I tend to rise on their list of respect when they see I'm north of average when it comes to cock size. That certainly was the case for me as a high school and college student in regards to my peers, so why wouldn't it be the same in that situation?