I'll just choose some from certain shows. These are just the worst episodes of some animated shows I like.
Family Guy: Turban Cowboy, Call Girl, Big Fat, Seahorse Seashell Party, April n Quahog, and many more
Adventure Time: James Baxter, Betty
Regular Show: Bald Spot, The Longest Weekend, Fortune Cookies, Cruisin
The Simpsons: Love is a Many splintered Thing, Lisa Goes Gaga, Moe Goes from Rags, to Riches, A Tree Grows in Springfield, and SO many more.
American Dad: The Boring Identity, Kung Pao Turkey, For Black Eyes Only
South Park: The Hobbit, World War Zimmerman, The China Problem
Futurama: The Butterjunk Effect, The Futurama Holiday Spectacular, T.: The Terrestrial, Forty Percent Leadbelly