Ask her, "You waiting for someone? Can I drop you?"

She smiles, but she's not happy. Maybe you're just acting a little /too/ friendly.

"Yeah, I'm waiting for my fiance - and no thanks, I'm sure he can drop me, I don't need you," she says coolly.

Dang, she already has a /fiancee/? Well, that's about the end of the story then - get yourself another chick, kiddo.