Just use a few canned lines for now, after a while, you will understand the nature of it, and you will be able to come up with your own.
Usually, i think of it as refraining from what the chick wants or means, eg:
HB: Sorry
Me: No you're not
HB: Oh really?!? I love guitars too!
Me: No you don't, you just want a ticket into my pants!
HB: You have really nice tanned legs
Me: Yeah, but your gaze is moving up onto my crotch.
HB: I really hate your hat
Me: No, you're attracted to me.
Me: Well? Aren't you going to ask me out already?
Me: Don't do that, i don't want people to see the girl i'm with is embarrasing.
Stuff along those lines, come up with your own, its not that hard.