Haven't I seen you somewhere before?

A phrase used when one recognizes someone or thinks they look familiar. It can also be used flirtatiously when trying to start a conversation with someone that one deems attractive. Haven't I seen you somewhere before? You look really familiar. "Haven't I seen you somewhere before?" is Ed's favorite pick-up line, even though it has a very low success rate with the ladies.

Haven't I seen you somewhere before?

and Haven't we met before?

a polite or coy way of trying to introduce yourself to someone. Bob: Hi. Haven't I seen you somewhere before? Mary: I hardly think so. Bill (moving toward Jane): Haven't we met before? Jane (moving away from Bill): No way!