Get the PDFand ask yourself these questions every time you're flustered. The statement at the top, "Why are you always so happy? Because it feels better!" can be attributed to the Dalai Lama. I think what he meant, was that happiness can be a conscious choice.
Strangely, my initial reaction was to ponder if the converse held any truth. Upon reflection of my previous experiences, I really do think that anger can feel better.
That's when I remember some of my biggest arguments, and how I wished they would never end. In that way, I was experiencing an artificial high without having to exert any added cognitive effort. My mind was able to focus solely at the task at hand: to debunk the other person's arguments.
It's a funny sort of "flow" state to be in, where you're actively engaged and emotional. I can see why people seek it out (albeit subconsciously).
I think that the ability to become angry is a useful one, and I'd be damned if I'd suggest eliminating this remarkable ability; anger seems to be the trigger of many a revolution.
But I do think that if you're gonna get angry, get it under control, and make it feel good.