"Jumped the Shark" is an old TV reference from the show
Happy Days. It was number one in the ratings for years (or thereabouts.) Fonzie was so cool. Everyone tuned in. But the show started going downhill, losing viewers because the show was just on for so long.
So in a desperation move, or maybe smoking too much weed,

the writers wrote the most stupid episode where Fonzie, got on water skis and in some kind of dare, in his motorcycle jacket,
jumped over a shark.
Fonzie lost all his "coolness." The series went
completely downhill after that. And the show limped for a while & finally got cancelled.
Any time a show has an episode now, where you know the moment the series turned toward to it's downward spiral to cancellation & loss of viewers, is now known as "Jumping the shark."