No duh: Some men are bisexual.

Now, here is a humdinger: a study at Northwestern University recently "proved" that men can be bisexual, as opposed to just "gay but in the closet." The studied gathered 100 men, roughly one-third each of self-identifying as gay, straight or bi. The researchers then had these lucky bastards watch gay porn and lesbian porn and monitored their penises for arousal. It turns out, shockingly, that gay men liked the gay porn, straight men liked the lesbian porn, and bisexual men liked both. I know, it's crazy! All this time we thought guys who claimed to be "bi" were just really slutty. [The Week]