Hi, Teddy,
Been there, done that.
If I get into a beef with someone I usually try to mend fences, but often I will still harbour resentment. Then I will feel guilty about being dishonest and also guilty that I got mad in the first place. After all, we are taught from infancy that it is bad to express anger. So we grow up with no decent skills to deal with this very basic emotion.
I have to work hard to control my anger and express it in a clear, concise way without saying things that will burn the house down. If someone disrespects me, I will generally turn my back on that person forever. Grudges are not very nice pets; they take up alot of space and they $#%^ on everything. One way I let the anger out when it is just not receding is to write down the entire episode in detail. This helps clarify and vent.
If the person is someone I really want to continue having in my life, I will try to forgive the transgression. But I will also make it clear the person involved shouldn't do it again.
If you have a confidant who is neutral with whom you can talk about your unresolved issues, do so. I am so grateful to have my partner, who has listened to my many anger issues. If my partner is the one who pissed me off, I will talk to my best friend, or write it all down. I have a private folder on my PC full of rants!
Good luck with this bottled up problem. I hope our anger coach weighs in on this. I could use some help on this, too. At least you are not alone in having this problem.