Really depends on the situation, as it involves another person or group I usually just take a look at what's going on from their end, and understanding it makes me feel silly to be angry anymore.
If it's just generic me-being-pissy-ness (hey, I'm a redhead, it happens... often), then I usually just start Monster Hunter on my PSP and pick the hardest monster my rank will let me fight. As good as it feels to beat the crap out of things with the massive weapons, blind rage doesn't make you last very long so I have to force myself to calm down and think properly.