Why is it that men openly adjusting/grabbing themselves in public is socially acceptable?

I get that dangly bits need adjusting. I sometimes have to adjust my bra and my boobs, but you know, I try to do it surreptitiously. I am shocked sometimes at how openly the dick-tugging happens and that no one seems to bat an eyelash. I find it really gross and somewhat offensive. I mean, where are manners if you can just openly tug your junk in public?