Do I have a case if I was told by one of my co-workers that my boss had said I had no common sense, which irritated me and insulted me?

Suck it up. One negative comment at work [except perhaps for a racist remark or other protected class] if not a basis for a harassment or defamation suit. Even if you could file, you would get to nothing in damages and your bosses would consider you a trouble maker, so you would be the first let go in any reduction in force. Your boss now knows not to make that type of remark. If you go to a higher up, they will just tell him to be careful in the future and think that you have no common sense. People get insulted all the time and unless it is really vicious you have to learn to live with it. Haven't you said something negative about someone else do you think you should have gotten in trouble. Your boss was honest enough to admit it, which many would not.