What besides being insulted in childhood due to a weight problem could make that adult so painfully insulting to others?

Does a person become awfully insulting towards others simply because he was teased in youth? I myself was teased and taunted due to early development but that did not turn me into an insulting person. I am just wondering what else could cause an educated and logical adult to hurl painful insults at other people who are not part of his problem. Pent up anger? Could that be the cause?