One of the most common biphobic narratives is that the penis is what counts. A woman who has sex with men is really straight, even if she also fucks women; a man who has sex with men is really gay, even if he also fucks women. If a man fucks a man, even once, he is forever corrupted from the heights of heterosexual masculinity.
Bisexual Men, Like, Exist And Stuff | No, Seriously, What About Teh Menz?

(по ссылке из нежно любимого мною блога sex is not the enemy - осторожно, рейтинг!)