* BaseBreaker: Chachi-nated, or De-Chachi-nated? Nick at Nite even made a marathon out of this premise, and viewers got to vote.
* CrowningMomentOfFunny: Fonzie's been using "Sit on It!" for years, to great reaction. When ''Marion'' of all people uses it on ''him'', the reaction from the crowd and Fonzie himself was priceless.
* DarkerAndEdgier: By the final season. Well, as D&E as you could be with this show. More dramatic moments (among them an AttemptedRape of Joanie), the use of "hell" and "damn", and Fonzie showing more weakness.
* EarWorm: C'mon, sing it with me: "[[TitleThemeTune Sunday, Monday, Happy Days...]]".
** The "Pumps Your Blood" song.
** Fonzie in the first two seasons, so much that he became a BreakoutCharacter and was promoted to second billing, after Ron Howard.
** Mork was only supposed to be a one-shot character and his episode AllJustADream, but RobinWilliams' performance was such a hit that the episode was revised to make the events real after all and gave him his own spinoff.
* HeyItsThatVoice: Apparently Ralph Malph ends up [[WesternAnimation/DungeonsAndDragons stuck in The Realm working for Dungeon Master]]. Who knew?
* ReplacementScrappy: Roger.
* TheScrappy: Roger.
** Chachi was ''always'' [[TheScrappy The Chachi]]. He was popular with the girls, but retroactively, amongst older fans? Please.
* SeasonalRot: It started out as a very cool, low-key show, then became the ideal version of a standard sitcom with a StudioAudience. It'd started getting worse (the Trope-Named Shark-Jump) even before Richie left, but only got worse after that. Fonzie got a temporary full-time girlfriend for one season, and things got increasingly worse with gimmicks and nonsense until a thankfully fantastic final episode.