Channeling strong emotions into writing has been done since the world began. As you'll discover, channeling rage or sadness into anything creative is rather difficult. When people feel emotionally compromised, usually they'd rather go punch something (or somebody) or drink something strongish. Sitting down at a computer and writing another chapter in Farewell Atlantis seems like the last thing you'd want to do. The hardest part is making yourself sit down do it.
Say you've had an incredibly frustrating day. Lets also say that your solution (or self-imposed therapy) involves some kind of writing, whether it be poetry, fan fiction or something else entirely more violent. If you're trying to write something other people will actually want to read, it's probably best not just to write MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER MURDER until your fingers bleed. It certainly feels nice, though. You could also channel your rage/anger/frustration into a violent murder story that involves you killing all of your coworkers, but that's the kind of thing the FBI regards as suspicious.
It's probably best if you try to use your newfound emotional power for good instead of evil. It's kinda like a super power, actually. A super powers that is actually rather common. Your secret power, however, is that you know how to use it.
Assuming you're focusing on a particular person (whom you're angry at) or an emotion (directed at the person you're angry at), that's probably what's going to come out of your writing. It's a little bit like catching lightning in a bottle; if you do it right, it's amazing. If you do it wrong then you'll die (your mileage may vary).
Be prepared to clean up a lot of things. I find that I write more than I need when writing from an emotional place, and so many things end up getting deleted. As always, however, it's better to write too much than too little.
Another benefit of writing angry is that you'll almost never be bored. Everyone has had those days where they sit down at the keyboard and stare at a blank screen (or notebook) and think, “I can't write today.” When you're angry, the reaction is more akin to “LETS WRITE A BATTLE SCENE!” or “AVALANCHE ON A SKI SLOPE!”
If you find that you're still unable to write anything with a semblance of a story, you can at least try to write down character descriptions or story ideas. Sketch the aspects of the person you're mad at with broad character strokes. Maybe you can narrow down the things you're mad at and distill him down to pure evil. Who knows, you might have just made the next Great Villain™.