Lucky asked in another thread how a bottom can be bi.
It's simple:
1. With guys I like big strong aggressive guys who are all man. If they were willing to take it up the ass from me or suck my cock it would blow my illusion of them as "more masculine than I am" which is what appeals to me about gay sex - submitting to a stronger male.
2. With girls I don't like them strong or muscular. In the same way that if I'm going to be with a man I want him to be all man, if I'm going to be with a girl I want her to be feminine and submissive and all girl. Otherwise, what's the point? And the idea of a girl with a strap on is visually ridiculous to me - so I'd rather just fuck her face or take her from behind and slap her ass.
In other words, I don't want to do things halfway.