As a male, I've learned long ago when I step up to a stall next to another dude, I'm not supposed to look at their genitals. As it turns out, dudes don't like when other dudes look at their junk. As a result, I've never had another dude showing me their genitals in a men's room.
Come to think of it, if I had a choice, I'd probably rather a woman looked at my junk in the bathroom than a dude...