Depends on what I'm stressed about. Usually I just focus on dealing with whatever's making me anxious asap so I can stop stressing over it. If it's something abstract or just something I can't deal with, though, I'll listen to music or doodle cute stuff in mspaint. Usually both at once.
If I need to vent, often times I'll go play duel (usually under alias so nobody bothers me) and just release my frustrations there.
Sometimes it's better to drop whatever that's causing you to feel awful and just take a moment to distract your mind and realize it's not a big deal. It's smart to know when to stop for your own sake, sometimes things aren't as important or urgent as we believe them to be in the moment.
I also second this.