Although I am not by nature an exhibitionist, neither am I uncomfortable having my parts be seen by other guys under most circumstances.
I have no problem with things like medical situations, changing or showering (although I haven't been in that situation since the military). My parts have also been on display to strangers of both sexes at swing clubs and parties, as well as the obvious posting of any photos here; which I'm fairly certain is viewed 99% of the time by other men.
What I do not find acceptable is when there is obvious intentional leering of those parts under circumstances that should be non-sexual like the aforementioned showering or changing clothes or at any time when just trying to take a piss. Although the urinal obsession seems to be Numero Uno fantasy of the LPSG crowd, I prefer one just accept I have a penis like every other guy rather than particularly breaking their neck trying to get a glimpse of it.