Definitions
1.NounSomething unexpectedly said or done which causes shock or offense; an insult, rebuke, or rebuff."That Joan's ex-boyfriend turned up to the school dance with Mary was a slap in the face for Joan, and the girls are no longer friends."
2.NounUsed other than figuratively or idiomatically: see slap, in, the, face. (This sense is a translation hub.)
3.VerbTo insult or offend unnecessarily.
4.VerbTo be or suddenly become bluntly obvious to.