Teacher's Pet (Season 1, Episode 4):

Angel: (smiles) I heard a rumor there was, uh, one less vampire walking around making a nuisance of himself.

Buffy: There is. Guess I should thank you for the tip.

Angel: Pleasure's mine.

Buffy: Course, it would make things easier if I knew how to get in touch with you.

Angel: I'll be around.

Buffy: Or who you were?

Angel just smiles and moves around to the other side of her.

Buffy: Well... Anyway, you can have your jacket back.

Angel: It looks better on you.

He turns and leaves. Buffy stares after him. Angel gives another look back and disappears into the crowd.

Buffy: (to herself) Oh boy!