A deeply rooted fear that one of your "bros" or you, your bro-self, might be gay.
Dave: "Holy shit Kyle, why do you have gay magazines?!?!"
Kyle: "Dude it's for style tips, the chicks dig gay dudes!"
Dave: "Whatever bro, that's so gay!"
(Dave is suffering from Bromophobia, and he may even be gay himself, as many bros are)