Way I see it, it's about context. Genitals don't (as far as I know) exist by themselves; they're attached to people, our experiences with them, and other things.
I find vaginas much more attractive on a big, burly bear than on a woman. In fact, women/femininity kind of ruin vaginas (or cocks, if we're talking about a woman with a penis) for me.
So it's easy for me to conclude, since I find masculine traits a turn on and feminine ones a turn off, that gay describes me better than bi, even if it seems a little counterintuitive that painted nails on a guy can make him less attractive to me than him having a pussy.