Two approaches that have worked well for me...
The first one is one I got from David Deangelo:
When she asks to take your order reply with "I'll have the usual" in a serious, normal voice. When she replies back a bit confused and says she doesn't know what you're "usual" is, shake your head in an slightly exaggerated manner and serious, yet playfully say, "You don't know my usual? You have a pretty bad memory! I don't think this relationship is going to work.".
Continue playing with her from there, get her email/number and get your food. When you leave, do NOT try and go say bye to her. If you happen to see her on the way out then a small smile with a nod of the head, or a short "bye", "see ya", whatever is cool. But please don't go back up just to talk to her again or say good bye. Just don't.
Another approach that I just LOVE to do is one that with either really piss off the girl or make her laugh. You'll quickly tell what type of person she is by her reaction.
When I'm a store (doesn't matter what kind) and the girl is cleaning up, say sweeping, I'll walk by and say in a serious tone, "Hey, you missed a spot" and i'll point to the spot. She'll look at the spot, then look at me like "No you didn't!". I'll give her a sly little smile and go from there. Sometimes they look at me with daggers in their eyes, hahah. Sometime they bust out laughing or they'll reply with something witty. If they reply well, I have some fun with them and get their info. If they reply upset I just say, "Hey man, don't get an attitude with me. I'm just trying to help YOU out.". Then I laugh at them for a sec and leave. hahahah.
-Shadow