“Humor! Ar ar ar.”
Not That There’s Anything Wrong With That
yada yada
Could I be anymore in to Seinfeld?
Hey, Hey, Hey!
“Sweet Baby Jesus” in a quavery Southern voice. It was Sissy’s (Beth Grant) major catchphrase from Sordid Lives.
Shoot them all and let God sort them out. (Marge Simpson)
Not exactly a sitcom, but there are a few from Animaniacs I can’t get out of my vocabulary:
“Woah, dumber than advertised.”
“Hellllooooooo NURSE!”
Giggity.
When I want the boyfriend to know I’m slightly irritated with him but I don’t want to be too bitchy he gets a “Hello Newman”.
Other Seinfeldisms:
“Sweet Fancy Moses”
“But I don’t want to be a pirate”
“Get out!”
“Helllllloooo”
“Oh no” said Phoebe style on Friends.
“I know!” said Monica style on Friends.
I know there’s tons more but my brain is on a break.
“Get outta hyeah” (with a Blanche Devereaux accent).
“Gooood one” (me thinking Roseanne Conner).
Numbering things as (1) and (b) or (a) and (2) like Paul from Mad About You. Admittedly I do this far more often in text than in speech.
“So’s your face!”
“You got some 'splainin to do.”
Quotes used in my family:
“Good news everyone!”- Prof Farnsworth- Futurama - Used when we have something bad to say.
“You just lost 5 bucks.” Bender- Futurama (He sold his body and was only a head lying in the street. A dog comes up and he says “I’ll give you 5 bucks if don’t pee on me.” Then we hear him say the quote) - used when someone doesn’t do something we asked.
“A story like that comes along once, maybe twice.” Burt Campbell-Soap- The family was sitting around exchanging nice stories about the late Chester Tate (or so we thought), nobody can think of anything nice, so Billy Crystal tells a story about Chester’s shoes that is dull and pointless. Burt sarcastically says the quote. We use this one a lot when someone tells, well, dull and pointless stories.
“Cafa-gyma-torium” - Everybody Loves Raymond - Used in reference to a school’s multipurpose cafeteria/gymnasium/auditorium.
Actually, a good percentage of my family’s conversations are quotes from Seinfeld, Spongebob, 30 Rock, Simpsons, Futurama, commercials, etc…Maybe we should read more.
“So’s your face” always makes sense. 
“Sweet something …of someplace…” and other variations of Hermes’ catchphrase from Futurama.
My favorite being “Sweet guinea pig of Winnepeg!”.
The one from the thread title.
Well, Top Gear isn’t a sitcom but they do have some catchphrases of sorts. To be used in the face of some clearly absurdly difficult project/task:
How hard can it be?
“How you doin’?” from Friends.
Said by my brother and I whenever we see someone good looking. We also say it sometimes just as a greeting to each other.
(Introducing the Stig) **Some say **he invented Betamax, and its subsequent failure is the reason why he never talks.
“I knew it!” said Chandler style on Friends.
“…anyway…” said Ross style on Friends.
We also usually order a “Joey Special” when we get pizza.
“OH–MY–GOD” said Janice style on Friends.