Some cosplayers are nice, know few of them, they like to do fucked up shit just because they get "bardoned" by the fact that they are.. cosplayers.
Once they dressed as batman and robin (oldschool style tights) when they went in to a rave and they had "anti rave spray"-can with them, that was fucking hilarius.
But guy cosplayers who dress like some anime girl are just more wrong than Hitler.
:edit: I'd go as Alien from movie Alien and I'd eat you all. Nobody messes with them.