If you describe something that someone does as a slap in the face, you mean that it shocks or upsets you because it shows that they do not support you or respect you.
'The Sun' calls it a massive slap in the face for the government. [+ for]
Britons persist in treating any pay rise of less than 5% as a slap in the face.
Synonyms: insult, humiliation, snub, affront