A scoffer does not like to be reprimanded (Proverbs 15:12).
Hardly anyone is as thoroughly condemned and treated as contemptuously as the scoffer, who behaves with scorn and ridicule. King Solomon does not condemn a rasha -a sinner - as much as he does a scoffer. The rasha of Proverbs sins by indulgence - by submitting to temptation - and thus is tolerated, though criticized. The scoffer, who acts with derision, is totally rejected, much like the "wicked son" mentioned in the Passover Haggadah.
Those who sin because of temptation are redeemable. Someday they may realize the folly and futility of a life of self-indulgence, and then they will do teshuvah and turn themselves toward spirituality. Not so scoffers, whose attitude of mocking everything puts them beyond redemption. As R' Moshe Chaim Luzzato says, "The scoffer can be compared to a shield coated with grease, which causes oncoming arrows to slip off. Likewise, scoffers are immune to reprimand and direction, not because of any lack of intelligence, but because of their attitude of derision, which destroys every ethical concept" (Path of the Just:5).
Criticism may not be pleasant, and not all criticism must be accepted. Sometimes, the reproof we receive may be incorrect, and we are actually right. But we must always listen to criticism and then make a proper decision. Frank rejection of reproof without giving it serious consideration renders us beyond help.