Boy, I relate to finding that kind of baiting irresistible! My trigger was the story he kept telling me and everyone else that I had partied in San Francisco to the extent that I had such a huge hangover that I was in the bathroom for the entire transatlantic flight. The truth was that I became horribly stomach sick after eating oysters two hours before getting on the plane.
I used to get SO enraged when he'd bring that up, because it was so non-sensical, irrational, and not to mention it was an attack on my character.
So I understand your feelings big time. It's so frustrating. In your case, it's even worse because it drags your son into it. I think GettingBy has a good suggestion. If that can put an end to his craziness where it concerns your innocent child, that might not be a bad idea.