Reciprocative Feelings

[LateBloomer]

I'm surprised no one has mentioned eye contact (sort of assumed as part of "gay-dar" I suppose).

But if another guy tends to hold your gaze, chances are he's EITHER:

1) Interested
2) Trying to place your face (thinks he might know you)
3) Has poor eyesight and doesn't realize you're checking him out.

So, eye contact isn't 100% reliable, but it's a PRETTY GOOD indicator.

Example: The guy I've been seeing lately, I met online. I asked him once, "If I met you in public would you have flirted with me or tried to talk to me." (I'm very "straight" in my manners and speech). He said, "No, not unless you made eye contact with me."

Try it.
Good luck.