As you know, I believe that Happy Days incorporates more shark-jump points than any other show. So when I watched the fourth season DVD (coming out tomorrow, and with all the music -- surprisingly -- intact and paid for), I was actively looking for other moments that could be seen as shark bait. And I found one: a scene that I remembered as being a possible JTS moment occurred midway through the fourth season. (The Pinky Tuscadero thing is also a definite JTS possibility, of course, but that's the season opener.)
What's JTS-y about this scene is that it takes all the gimmicks of the Fonzie character and incorporates them into less than two minutes of screen time: he inexplicably shows up to save Richie; turns an evil woman good with one snap of his fingers; performs some kind of impossible feat of strength; makes the jukebox play "Put Your Head On My Shoulder" by hitting it. By having all these clichés go off at once, the writers finally completed the transformation of Fonzie into a cartoon superhero, which is what he would be in the actual Jump the Shark episode. So this is, arguably, the moment when Fonzie became a complete parody of himself, and that's a possible definition of a JTS moment.
Are there any other moments you can think of that struck you like that -- where a show put in so many gimmicks and catchphrases at once that it seemed to have gone too far? I know there are lots of characters who turned into parodies of themselves over the years, but I can't think of many who had one specific moment of transition. The only other one I can think of for now is Xander on Buffy the Vampire Slayer, who instantly went from the best character on the show to a bad pod-person parody of himself when he had the slap-fight with Harmony.