Suppose you are a bad person. You get angry a lot, have trouble valuing much, aren’t very successful, blame others for your troubles, and hurt your children often. But, whatever, you’re life isn’t so bad. You get through it, enjoy a fair amount of it.
Now, suppose someone claims to be moral, and you notice the implication that you are not. And suppose this person lacks all your bad traits. This might well make you feel bad.
And then you might write a letter to the so-called moral person, attacking him. The content might be along the lines of (if you were exceptionally intelligent and clear, for a bad person): You bastard, fuck you. You’re totally wrong. Oh, and if you reply in kind you’re just like me, except also a liar. Nope, just sit there and take it, Mr. High and Mighty. Oh, and you can’t get resentful because that would violate your moral code, huh? But you are mad at me, aren’t you? Yep, you’re a hypocrite. Now stop implying I’m bad, and get back to your stupid, lucky life.