"Bitterness is the result of not forgiving others. If you are bitter at someone, it means that you haven't truly forgiven that person. ...
Bitterness is the result of dwelling too long on a hurt.

Evidences of Bitterness

1. Difficulty in resolving conflicts
2. Acts of vengeance
3. Withdrawal
4. Outbursts of anger
5. Biting sarcasm
6. Condescending communicaiton
7. Criticism
8. Suspicion and distrust
9. Intolerance
10. Hypersensitivity
11. Impaitence
12. Disrespect
13. Rebellion against authority
14. Misuse of authority
15. Depression
16. Doubts regarding salvation
17. Remembering with great specificity the details of an offense."

[Lou Priolo, "Bitterness"]