I'm straight and have a reasonably well-tuned gaydar for gay men, whether they look or act femme or not, as long as I have the chance to interact with them for a few moments. I've found that gay men respond to me as a woman in a completely different way, generally, than straight men do. The gay guys I'm acquainted with have a way of looking right through you without the same sort of check-out appraisal technique straight ones employ. It's almost unconscious on their part, but it's an absence of interest on a very basic level that gives them away every time.

I'm far less well able to identify gay women or bisexual people of either gender. And I mostly don't care about identifying anyone one way or the other, now that I think about it. What matters far more to me is whether someone is kind. Or intelligent. Or caring. Or funny.