Stinging insult? (4,2,3,4)
'insult?' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
(Other definitions for slap in the face that I've seen before include "the result of stupidly eating pancake?" , "Unexpected affront" , "Unexpected rejection" , "Insult" .)
(Other definitions for jab that I've seen before include "Short stiff blow or thrust" , "Inoculation" , "Prod" , "Short straight punch" , "A short stiff punch" .)