Slap In The Face Meaning

(figuratively, idiomatic) Something unexpectedly said or done which causes shock or offense; an insult, rebuke, or rebuff.

Example: Used other than as an idiom: see slap,‎ in,‎ the,‎ face.
  That Joan's ex-boyfriend turned up to the school dance with Mary was a slap in the face for Joan, and now the girls are no longer best friends.