I don't know about you, but nothing robs my joy faster than an irritation that could be avoided if the other party would play fair.
The easiest of this example is in driving. When you've waited in the long line of cars to exit and someone comes speeding down the right side and then tries to cut in. It makes me want to get out of my car, and punch that person in the face. It is a red-hot anger irritation. It is also something that seems to be unavoidable and constant.
I will be the first to tell you that I don't yet have the tools or help to fix this yet. But I suspect that part of it comes from the Enemy. If you are entirely focused on the irritation then it is hard to see the other things around you. It puts you in a foul mood in which you take it out on everyone else. I'm sure you've seen the commercial depicting this very thing. The hard part is when you realize your actions were the one that caused the downward spiral.
To help keep me from going into this vicious cycle is I sing. At the top of my lungs. No matter who is in the car. If it is the President he should sing along. If you have a bad voice all the more reason others should join you in a loud chorus. If you don't like singing I suggest screaming. I recommend this even if someone is in the car with you. Encourage them to scream with you. It may very well seem silly at first, but once the focus is off of the irritation the easier it is to get that joy back and see the Enemy fail.
I sing whatever is on the radio or MP3 at the moment, but I find this song helps ease my anger a little bit:
Take a Look Around (Mission Impossible 2)
by Limp Bizkit
That's right Limp Bizkit. Don't ask questions. Just sing.
"I know why you wanna hate me
I know why you wanna hate me
Now I know why you wanna hate me
Because HATE is all the world has ever seen lately."
So now, even though you're being a jerk I will be nice to you. So, there!