I only remember Fonzie jumping the shark in the episode. I remember nothing else from it. What made it so bad that it's the origin for the term "Jump the Shark" when a show goes downhill?

It's just that the plot was so absurd. Fonzie was competing with this other guy to see who was the better water skiier, and the final stunt was to see who had the guts to attempt to jump over a caged shark. It's regarded as the point in the series where the writers were starting to run out of ideas.

The episode was Hollywood Part 3 (of the three-part 5th season premiere) which first aired in 1977.

And I have a confession to make: It was me who actually jumped over a shark. I did it a long time ago.

i didnt think the epside itself was so bad, but the part with the Fonz wearing his leather jacket and boots on the beach with the white T-shirt and shorts was pretty unsettling.

...and the idea that the Fonz could instantly water ski better than a champion was kind of a stretch - at least when he dueled or danced or whatever he learned those skills from a girl he used to date.