I have a lot of experience with letting go of resentments. Once, when I was 7 years clean, I let a resentment get so bad I resorted to violence (after feeding the resentment for months), and got arrested and spent 4 days in jail - clean. Needless to say I wasn't working much of a program at that time. The other person got away with what they did to me, of course.
These days, when I get that angry, resentful feeling rising up in my body, I think, "Oh no! I have to lose this resentment ASAP." and I just start praying for God to help me. It's like that old game, "hot potato" where you have to get rid of the hot potato before you get burned. It helps to ask myself if I ever did whatever it is the other person did to **** me off. Did I ever do that to somebody else, or something similar, or did I ever just act like a total creep, did I ever really hurt somebody, etc... these questions make me realize how much we are all flawed and who am I to not forgive...