I used to bottle it up and I still do a pretty good amount of that, but I'm slowly working on changing it. Now, whenever I'm pissed off I go work out until I'm dead, then run as far as I can, then (now that it's summer) go swimming in my apartment's pool. By the time I'm done with all of that, I'm so exhausted that whatever had me angry isn't such a big deal anymore. Given how frustrating my work can be at times, I'm getting in pretty decent shape
I've also got a punching bag that I will occasionally pound the crap out of - just depends on the mood at the time.