TV characters that are annoying/stupid and/or frustrating to watch.
Urkel, from Family Matters
Mork, Mork and Mindy
Potsie Weber and Marion Cunningham, dumbed down in the later seasons of Happy Days
Britanny, from Glee
Doug Wilson - Weeds
Any professional (Lawyer, doctor, etc) in the show Arrested Development was meant to be played as so frustratingly incompetent that the viewer would be severely annoyed if they didn't accept the joke.
Jim in According to Jim owns this thread.
Lucy, from [italic]any[/italic] of the Lucy shows ("I Love Lucy", "The Lucile Ball Show", etc, etc)
Christopher McDonald's character on HARRY'S LAW. I can't sit through the show because of him
The entire cast of "Big Bang Theory", Cliff Huxtable. Patty Lane who cheated on her boyfriend almost every week. Charley Harper.
Any characters played by Richard Deacon and Jeffrey Tambor.
The entire cast of Melrose Place was the dumbest bunch of pretty people ever on TV.
Mrs. Constanza fron Seinfeld. I can watch her because she can be funny but that voice. Yikes.
Glee, the entire cast.
Richard Dreyfus in just about anything (with "Jaws" being the exception)
Michael (the boss) from The Office
Ted in How I Met Your Mother, the most boring central character in the history of tv sitcoms.
That Joe Izuzu guy from Empty Nest
Not sitcoms per se, but Ally from Ally Beal and Meredith Grey from Grey's Anatomy were also exceedingly boring/annoying.
Jerry Fucking Seinfeld.
Even typing that fool's name makes my blood pressure go up 20 points.
The characters from The Big Bang Theory.
Schneider (One Day at a Time)
Mr. Bentley (The Jeffersons)
Carlton, the Doorman (Rhoda)
Aziz Ansari's character could be removed from "Parks & Rec" without leaving a ripple. The rest of the ensemble integrates naturally in story lines, and he's always got some subplot that has nothing to do with any of them.
His entire performance is a variation on making this face.