The beasts

Apart from the optimists, there's also another king of people that I loathe: those who take on innocent bystanders their frustration and despair. No one has to bear with it; as angry as we might feel sometimes, we have more than enough mental capabilities to keep us from lashing out at others for no reason. That might as well be one of the things that defines us as rational animals, and marks the difference between us and the rest of the living creatures. If one willingly and deliberately decides to ignore all this to keep lashing out at everyone, then what exactly is the difference that separates that person from the beasts?