Anytime a TV show (usually a sitcom) starts to focus on just one character, that is the first sign of a shark jump.
Happy Days did it with their focus on Fonzie, Diff'rent Strokes did so, when it became all about Arnold, Family Matters became the "Urkel" show, and as you mentioned, Good Times centered around JJ. And in each example, that main character had a catch phrase that he seemed to say at the drop of a hat!
"Aaaaay!"
"Whutchu talkin' 'bout?"
"Did I do that?"
"Dyn-o-mite!"
It was almost to the point that viewers were disappointed if that main character didn't drop his catch phrase in there somewhere! And you would hear it at least once per episode! I'm sure that the writers of these shows probably hit on these catch phrases by accident, but continued to use them because of the audience reaction to them.