Haven't I seen you somewhere before?

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.
See also: seen, somewhere
Farlex Dictionary of Idioms.

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!
See also: seen, somewhere
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • be out of (one's) league
  • be out of somebody's league
  • (one) puts (one's) pants on one leg at a time
  • bell, book, and candle
  • bell, book, and candle things that are miraculous or that signal that
  • be (not) a patch on
  • bolo
  • a happy bunny
  • a happy camper
  • bring (someone or something) before (someone or something)