What you do is get a piece of paper or a computer and you write that person a You Bastard letter. In it you put everything that has made you angry. Don't hold back. "You did this.." "That wasn't fair.." "How dare you..?" Call them names. Say what you'd really like to say but you know if you did it'd create too big a rift to fix.
When you're done, print it out, fold it up and put it in your pocket. Every time you start to stew on your anger with this person, pull out the letter and read it. It will make you feel better.
After a few days, the things you wrote will start to seem silly, childish, over-dramatised, etc. When this happens you can burn the letter because it's a sign that you're over being angry and you can probably go discuss the problem with the person without having a huge fight. Or you just don't care any more.
I just wrote one. I feel better already.