Stinging insult? (4,2,3,4)

I believe the answer is:

slap in the face

'insult?' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for slap in the face that I've seen before include "the result of stupidly eating pancake?" , "Unexpected affront" , "Unexpected rejection" , "Insult" .)

I've seen this clue in The Times.

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