From “Seven Deadly Sins: The Biology of Being Human” by Guy Leschziner
People who are generally more angry pay much more attention to stimuli in their environment that are associated with hostility. They are more likely to pick up on perceived hostility or potentially anger-inducing stimuli than others. Whereas for most of us the scowl of a passerby may go unnoticed, for those where anger lies just below the surface, it may act as a trigger.
It is not just a matter of increased sensitivity to provocation, however. Impulsivity – the tendency to act without thinking – is also an important factor. When angry people find themselves in anger-promoting situations, they respond even more impulsively with anger.