When I was in residential treatment this last summer, they had plastic bats they allowed you to use. They called it "bat therapy". Whenever I got really pissed or had the urge to self harm, I would grab the bat and beat the hell out of the tree. Of course this did damage to the bat, not the tree, but it got so much of my aggression out. Unfortunately, it's more difficult to do if you don't live on your own property. Something else I had to try was screaming into a pillow. That released anger as well, and then you start to feel whatever was underneath that anger. Just be prepared to lose your voice if you try that.