Why do I let work make me so angry?

I started the day off just fine – had a great meeting with my boss, and then my day went downhill. Someone I thought was a great colleague was very disrespectful, then I caught attitude from vendors we are paying to help us, then I was told by a coworker that my last two predecessors were let go for not dealing with problems I was facing today.

Great, just great.

I hate my job today.