From Longman Dictionary of Contemporary Englisha slap in the facea slap in the faceOFFENDan action that seems to be deliberately intended to offend or upset someone, especially someone who has tried very hard to do something → slap
Examples from the Corpus
a slap in the face• But choosing that particular moment to do it was a rebuff as callous and shocking as a slap in the face.• It is a slap in the face and an insult.• Barnes's decision therefore came as somewhat of a slap in the face to these well rehearsed points.• And make no mistake: He considers the Padres' offer a slap in the face -- even mimicking such a blow.• Gwynn considered the salary they were offering a slap in the face. 