I tend to do a few things, depending on how stressed I am.
If I'm really, really stressed, I go to Starbucks or the local Chinese place. I could be having the WORST day of my life, and I go to either of those places, I quickly forget why I was ticked in the first place, or at the very least, I'm not as ticked as I was.
Starbucks, it's all about the caffeine. I'm a cheap drunk(or hyper, in this case), so a good coffee and something sweet has me calm and giggly to my husband's amusement. The Chinese place has a good, quiet atmosphere where you can sit, and the people who run it know us, and usually all it takes is some soup, sweet & sour chicken and a pot of tea and I'm nicely mellowed.
If I'm not as stressed, or just irritated and need to blow off steam, I play videogames, usually Battlefront II or Bounty Hunter, depending on what I'm in the mood for. There's something about blowing the crap out of things that can be very therapeutic, particularly when I'm blowing up a particularly STUPID videogame baddie.
There's one particular scene in Bounty Hunter with three baddies standing around looking very stupid when I have Jango standing not terribly far away(enough that were I up where they are, I'd be seeing anyone where I'm standing). A well-placed rocket not only obliterates them, but it's highly amusing to watch them looking around as the rocket's incoming.
So find a good videogame and blow things up or beat things up, depending on what your fancy is. It's a good stress buster when you can't actually go out and kick the snot out of it for real.

Hot baths also work for me. I like hot tubs, but that only works when I'm at a hotel somewhere. At home, I go for a nice, long bath/shower and maybe a cup of mandarin orange tea English style(ie: with milk in it). Eating chocolate also works.

Or find a favorite song. Music can help me at times, too.