People who can't be criticized--and who react with great hostility at any hint of criticism--are revealing something important about themselves.

They reveal that they don't hold their convictions and viewpoints about various matters through carefully reasoned out, fact-based judgments. Instead, they form conclusions based on emotions. Naturally they feel threatened when one of these irrationally based conclusions is questioned by a thinking mind. In a sense, they expect you to respond to their emotions as they already do: By treating them as equivalent to truth.