Ask him out if he says yes then he's gay.<br />
Also, why the does it matter?
so ask him out, if he says no forget him, there's plenty of gay and bi guys out there.
Just ask in a polite way?
If he isn't gay it sounds like he is at least comfortable with it. No reason not to be open about things. You could flirt and see where things go.
Tell him you don't swing that way.
It would help if you provided some context. Can you explain why you have this question?
What if he is?
If he is good dresser he is