They were one of the most bitter and angry people I had ever met. They never had anything positive to say. A scowl accompanied their bad mood and poor attitude. Nobody could do anything correctly, or at least to their liking. Their words were often loud and filled with a seething anger that seemed to have no end.
While I do not know all the reasons for their anger, some things became more evident the longer I got to know them. Loss of a beloved family member at an early age, a strict father with an overly submissive mother, and a long list of painful experiences filled their past. Over time those feelings of hurt had turned into anger.
One mental health website states that people change their feelings of pain into anger because it feels better to be angry than to be in pain. I believe it also gives them a sense of control in a life that has been out of control. Finally, anger can distract us from feelings that bring us down.
I am sure there are other reasons, but my experience has been that most angry people are the product of pain. The hurt they once felt is now channeled into another emotion.
So, if you know someone like the person I mentioned, the problem may not be anger but hurt. These people need love and grace while being the most challenging person to offer it to. But sometimes, loving our enemies better results from understanding their background.