When Jim started mocking Ralph, doing a silly Ralph impression, I immediately had flashbacks to when he started making fun of Donga, and talking like a native-american caveman. iirc Jim mocking Donga like that was a major spark in Donga's downward spiral, because that's when I recognized that he started lashing out a lot more after that.
In this instance, though, it was WAY more evident that Jim was holding back for one reason or another, until everyone else had their takes on Ralph, and for a fuckin' while, too. It would make sense based on what Jim mentions lately, that he's mostly more into sitting back and enjoying the show, and I'm guessing he knew that poking at Ralph would get him involved in the action, instead of letting him laugh from the sidelines.
In any case, Jim's replies on twitter don't disappoint at all. Even on a playing field of passive-aggressive sniping, you can tell that Jim is having fun with it and Ralph is seething.