What causes a person to develop a bad temper? [I Hated My Childhood]

My mother had a terrible temper, easily triggered by almost any little thing. I walked on eggs in her presence. You could never really tell what might set her off. She once threw a chair across a restaurant because she mistakenly believed the waitress had brought salad dressing (on a lazy Susan) when she hadn't ordered it. During their marriage (which ended in divorce) she beat up my dad and sent him to an Emergency hospital three times.

How do people get that way? Have you ever known anyone like my mother?