Whatever the outlet may be, all this unresolved anger toward someone does nothing but show how sinful I am.
(1) It's not my place to deal out justice or retaliation. In fact, God explicity condemns me ever taking revenge into my own hands (Rom 12:17-21).
(2) Me bearing a grudge and being bitter is really like me drinking poison in hopes that someone else will die. i've really only harmed myself. i've turned red in the face, had payback fantasies, had my blood boil while they were around or being spoken of. All this energy hoping they get their just deserts. Yet how much sleep is he/she losing over it? My grudge-bearing hurts me, not him/her.
(3) I should be mature enough to let things go. Is it really that big a deal what that person said or did? On my deathbed, will I really still care what that person said or did? Does what that person said or did really matter in the grand scheme of things? Is whatever that person did to me really worth all this time and energy i'm spending bearing a grudge rather than enjoying continuing a relationship with that person?
(4) Even if I do think it's a big deal, i need to be honest about my own need for forgiveness. Am i really arrogant enough to think i'm any better in God's eyes than that person? Am i really conceited enough to think that i'm any less guilty and sinful in the eyes of God than that person is? Am i really proud enough to think that i need God's mercy and forgiveness any less than that person? Am i really so selfish to think that how that person hurt me matters more than how i've hurt God?
(5) Do i really want so much of my life and my time defined by what the person did to me? Do i really want to be owned and controlled by the hurt they caused me? Is that really how i want to spend my time and energy?
Bitterness, resent, unforgiveness, grudge-bearing--none of these are in anyone's best interests nor do they benefit the people who harbor them.