That Neithan guy seems like he came on just to argue & start problems, I get a bad vibe from him.
In baseball, it's 3 strikes and you are out. If he didn't already have a 100% record of being a jerk (4 out of 4 posts), I'd apply the 3 strike rule. I think in his case, you are correct to give him one warning and then ban him if he gets personal with Dejon (or someone else) again. Wonder why this guy is being like that, I mean Dejon has always seemed to be a very accurate, honest guy, and I'm sure he is giving us a truthful version of what happened & what he heard.
So in general I would go with the 2 warning and the 3rd time you are out as a TPO policy.