I have this so much! I get very frustrated and furious about little things, especially when I'm already anxious about something, and sometimes feel almost overwhelming anger toward other people. It often degenerates into obsessive thoughts that make it almost impossible to focus on anything but how angry I am, which just makes it worse.
I find it really helps to engage my mind in something that requires a lot of focus. Of course this can be difficult because I'm so angry that it's difficult to concentrate. What I've started doing is having conversations with an imaginary person in French (which I'm studying in school). Since it's not my native language, it requires work, and even thinking my angry thoughts in French helps calm me down and takes my mind off my anger. However, languages are my main Asperger's obsession, so this might only work for me. Thinking in French, even angry thoughts, also improves my mood because I enjoy it. I also find that listening to or even thinking about intense music--it doesn't even have to be angry music, just something fierce and powerful sounding--helps me channel the intensity of the emotion into something healthier.
This also means that I get very good grades in French