Ooh, tough question.
At its worst:
South Park: Formerly one of the funniest series ever, but the jokes in later seasons seem forced, take too long to set up, and kind of fall flat.
Saturday Night Live: Often silly and overacted. Proof that playing a caricature isn't always funny.
Last Call with Carson Daly: When the SIARPC interviews aren't good and you can tell the person opposite Jezza really doesn't want to be there, it's like this. And Daly's about as interesting as watching paint dry. Actually, no--that's a bit harsh. Paint has a personality.
At its best:
No Reservations: Stunning cinematography, a lovely window into interesting places and things I may or may not ever get to experience myself, and ascerbic wit.
SpongeBob SquarePants (...the earlier seasons), or maybe
Phineas and Ferb: Wonderfully creative with casts of characters that play well off each other. (Yes, I still watch cartoons...don't hate.
)
The Thick of It: Quick witted, hilarious dialogue, and not afraid to be brutally honest.
(Honorable mention:
Mythbusters. Because everything can be improved with a good explosion, a big mess, fire!, or something that's...not gone well.)