“Jump the Shark” has become such a part of the lexicon that nobody remembers it’s from “Happy Days”?
Well, it’s not actually a catchphrase from the show. Even if it was actually spoken in that episode, it wasn’t spoken with the meaning it has now, so I don’t think it counts.
Catchphrases from Happy Days would include: “Aaaaay!” “Sit on it!” and “Bucko”.
“That’s asinine!” Also Hank Hill. I’ve got my whole team saying it these days. We’re “technical editors,” and our job is to turn crap into English.
“It’s 7AM and already the boy ain’t right.” Hank Hill. We use that a lot about one of the dogs.
DH and I can hold entire conversations in nothing but Simpsons, King of the Hill, Futurama, and South Park quotes.
Get lost and it’s I must of made a left turn at Albuquerque.
It needs Bugs Bunny pronouncing it.
Wabbit season no duck season
Not a sitcom, but I’m quite happy to shoehorn “Go go gadget [whathaveyou]” in a variety of unsuitable situations. Not sexual ones, though. Never, ever sexual ones.
I also like “Is it going to make me poo, Jez?” from Peep Show. You probably shouldn’t use this romantically either.
“Read the small print on your cone-tract” is applicable in a variety of work situations, whilst “cock piss Partridge!” is a useful epithet. If you can’t muster up a whole Alan Partridge quote you can just stick “… Lynne” to the end of your sentence, i.e.; “I’ll have full sex with you, Lynne!” which isn’t a Partridge quote but you can’t tell, “full sex” being particularly Partridge term.
Oh, and there’s the perennial “sex people!” as an expression of alarm, and if you want to get into Brass Eye territory there’s “I’m talking NONCE SENSE” (whilst pointing to head and midriff).
… Thinking about this now I’m quite sure that most of the time I make absolutely no sense to anyone 
I use this one over and over but it’s from the Fall and Rise of Reginald Perrin rather than the Good Life.
Other favourites:
“I have a cunning plan …” in my best Baldrick voice (Blackadder)
Not a sitcom but “You will accept 200 Federation credits” with appropriate mystic hand waving and Jedi voice always comes in handy.
I had forgotten where my use of “She’s gone!” (or “He’s gone!” as the situation warrants) came from, until I was watching an episode of my recently Netflixed first season of The Monkees last night, and said it just seconds before they did.
Mine is bizarre. I say it all the time though.
“Well, you’re weak.”
Mostly to friends. The key is to manage the perfect matter-of-fact deadpan that Kramer delivers the line with.
…from Seinfeld. The entire glorious exchange:
George: I am not giving you my code.
Kramer: I’ll bet I can guess it.
George: Yeah, right.
Kramer: Ah, all right, yeah… Let’s see… Well, we can throw out birthdays immediately. That’s too obvious. And no numbers for you, you’re a word man. Let’s go deeper… What kind of man are you? **Well, you’re weak, **spineless, a man of temptation.
George: uh…
Kramer: But what tempts you? You’re a portly fellow. A bit long in the waistband. So what’s your pleasure? Is it the salty snacks you crave? No no no no… Yours is a sweet tooth.
George: I gotta go.
Kramer: Oh, you may stray, but you’ll always return to your dark master… The cocoa bean! And only the purest syrup nectar can satisfy you. If you could, you’d guzzle it by the gallon… Ovaltine!? Hershey!? Nestle Quick!?"
George: [running away] Shut up!