Guys: When you hit on a girl in a bar and she tells you she's gay, do you believe her?

Last night I went to bar trivia with some friends and this guy starts hitting on me rather ridiculously. I’m sitting in a booth and he nearly climbs into my lab, kisses me on the cheek multiple times, tries to hold my hand, whispers how cute I am into my ear, etc… I’m pretty gay, so I tell him so (politely!). To my surprise, his response is “I don’t mind.” and I (slightly drunk at this point) reply, “I don’t mind that I’m gay either!”

Anyway, he did not back down, even after asking if I have a girlfriend. (I said yes, although in reality it’s debatable, heh.) Luckily a friend eventually rescued me, although the guy looked very miffed that a butch girl in basketball shorts was getting more attention than him.

So why didn’t he leave me alone after I told him I was gay? Did he not believe me, and if you think he might not have, why wouldn’t he?