He was a career military guy who lost a son to gun violence. He was not supposed to be making jokes in almost every scene..
Personally knowing people who lost children at a very young age, you can give that a place in your life again and enjoy and laugh. It's not as if you must be a depressed maniac for the rest of your years. Granted, I became tired of the always joking O'Neill after a few years, and his performance did become routine. But saying that he was not allowed to have a happy life after loosing a child......