People who just refuse to indicate.
You ever see that scene from shoot em up, when the guy does not indicate and Clive Owen chases him down and does him in?
I get just about that angry!
What makes me angrier is when people give reasons such as they don't indicacte cause they don't want other selfish drivers to block their path...
Of course I'm not gonna hurt someone for doing that... I would just scream really loudly, and violently shake my finger at them, ha ha!