Mine would be:
The Simpsons
Alone Again, Natura-Diddily: While it had some funny stuff (I like most of the Mike Scully era episodes), killing off Maude was extremely pointless and in poor taste.
My Big Fat Geek Wedding: Basically undid the entire Skinner/Krabappel relationship, and stuck us with another cheesy Homer and Marge "marriage on the rocks" tale. What was the point of building up Skinner and Krabappel's relationship if they let it disintegrate liks this, and then tease us further about how Skinner can't get back with Krabappel?
Family Guy
Stuck Together, Torn Apart: One episode where Meg is used only for abuse. While it began as far back as Season 2, Season 3 is where it became a substitute for character development.
Model Misbehavior: Another with unfunny Meg abuse, and one that re-established Lois as a borderline whore.
Jungle Love: The worst FG ever. Poor, uneven story, terrible jokes (including two flashbacks that go on forever), and of course, more Meg abuse that ends with her "death".
It seems like whenever they do an episode that's mostly about Chris and/or Meg, they can't put it to good use, as if they don't even try.
Untitled Griffin Family History: The way Meg was treated was so terrifying that everyone in the family came off as a pack of villians, and it dragged this whole episode down.
Stewie Loves Lois, Mother Tucker, Boys Do Cry, Believe it or Not, Joe's Walking on Thin Air: All boring.
King of the Hill
Texas Chainsaw Massacre: Dale driving Hank crazy the whole time, even when his life was at stake.
Goodbye, Normal Jeans: Peggy acting like a lunatic, ruining Thanksgiving, and totally getting away with it.
Racist Dawg: Black repairman plays the race card, and the whole town is against Hank, even Peggy!
A Rover Runs Through It: The Hills finally make it to Montana (after failing once in Season 4), but an ongoing mystery regarding Luanne's family is completely ignored for a boring story about those "jerks from Hollywood messing with the environment" and such.
A lot of episodes from Seasons 9 and 10 are terrible.
Futurama
A Leela of Her Own: Somehow, this wasn't as cool as the other Futurama stories. It just wasn't.
The Proud Family
All of Season 3.
Each episode shifted towards unfunny abuse against Oscar, which quickly tuned me out of the entire series. I'm embarrassed at ever having watched this show.
The Fairly OddParents
Many episodes from the 4th and 5th Season.
Baby Face/Mr. Right: Two episode where Timmy's bullies get their "revenge" at the end, while Cosmo and Wanda happily watch their godchild get hurt. :sad:
Class Clown: One where Trixie is a crazy, ungrateful harpy, and where Cosmo is annoyingly stupid.
Just the Two of Us: I know someone thought "What if Trixie wasn't 'the one'?", but come on! Why did they have to make her a homicidal loon?