1
general::
A sharp rebuke or rebuff, as in Being criticized in front of my staff was a real slap in the face, or We thought it quite a slap in the face when they returned our letter unopened. The figurative use of this term, which can Also refer to a literal blow, dates from the late 1800s.
American Heritage Idioms
2
general::
Phrase(s): a slap in the face
an insult; an act that causes disappointment or discouragement. • Losing the election was a slap in the face for the club president. • Failing to get into a good college was a slap in the face to Tim after his years of study.
McGrawhill's American Idioms And Phrasal Verbs