From the three-part episode "Hollywood" (the opener of season 5), the story of how and why Fonzie jumped the shark. Featuring a shark, a leather jacket with shorts, lots of bad background music, Laurette Spang (who appeared on the show in season 1 as Richie's girlfriend Arlene), and a guy who thinks he's Jack Benny. Ayyyyyyy!
The most unintentionally funny "Very Special Episode" ever. That's not a knock on the actors, who are very good. That's not a knock on Suzi Quatro, who has a great set of pipes. But it's just so cheesy, exploitative and dumb. Plot summary: Richie is in a coma so Fonzie can cry, Leather Tuscadero sings a song that sounds way more like the late '70s than the late '50s.
A year after Fonzie jumped the shark, the show followed that up by having Fonzie ride a killer bull. This episode may actually be dumber than the jump the shark one.
The "Welcome Home, Richie" two-parter from the last season: Richie comes home from the army and his responsibilities may force him to give up his ambition to become a Hollywood screenwriter. One of the better late episodes.
Some of the more ubiquitous and annoying catchphrases from HAPPY DAYS. (Most of these are from the third season because they deliberately introduced new catchphrases that season.)
Suzi Quatro sure can sing, but if Chuck Berry saw Ron Howard trying to pretend to play guitar, he'd climb into a grave just so he could roll over in it.