In order for Jack to be considered off his rocker, you're suggesting he was actually on it at one time.
Or that he ever had a rocker to begin with.
Or that he even knew what a rocker was.
Or that the thought of anything that could possibly even resemble what we would call a rocker even existed in his twisted perception of reality. I think the existence of a rocker to Chick would be like dividing by zero to us.
There's one way to find out, but it involves something called "bath salts" and I don't want to try it.