What's your least favorite episode of a show that you like otherwise. For me, it's definitely the Spongebob episode "One Coarse Meal". Mr. Krabs is incredibly unlikable in this episode, as he almost drives Plankton into trying to kill himself (in a kid's show, btw).
There's lots of bad SpongeBob episodes. Lots of great ones don't get me wrong, but lots of bad ones, too. That's in contrast to Avatar: The Last Airbender (which I think is the greatest TV show ever) where the only bad episode is (IMO) "The Painted Lady". EDIT: Maybe also "The Great Divide" but I do think that episode isn't as bad as many say.
It's hard to pick just one episode but I'm going to say episode 27 onwards of Death Note because the drop in quality is pretty big. If you've watched the show you know why but I won't spoil it here.
The series finale of How I Met Your Mother was lousy. It almost poisoned the whole series that came before it.
I think the last episode of 'The Prisoner' was boring. It just seemed to be cars driving down a motorway.
Season 4 of Sherlock. Took the focus away from the case and to Sherlock himself, something I wasn't that fond of.
I also think the episode of The Loud House "No Such Luck" is atrocious. Lincoln, the main character, is considered bad luck by everyone else and is treated horribly throughout.
The worst episode of any long running series is a clip show. I don’t think The Simpsons produce these anymore, but they made a few back in the day. It’s just lazy programming.
The finales to Game of Thrones and Battlestar Galactica (reimagined series) are both guilty of this. Clip shows aren't really a thing anymore, or at least shouldn't be. Back in the day, they were a way for shows to fulfil a (usually) 22 episode order to fit in with US TV schedules, while holding back some cash for a blockbuster episode or two. Bigger TV budgets and less precise requirements for length and number of episodes in the streaming era have made them obsolete.
Now I feel like I will get a lot of flack for indicating that I watch Rick and Morty but I just feel like I have to say it. For Rick and Morty I am torn between "Pickle Rick" and "Rickdependence Spray". "Pickle Rick" is bad because it is the start of what I think is one of the current flaws of R&M which is that Rick has become a predictable and unstopable one man army. Rick was always strong but in the first two seasons he showed fear and vulnerability and ran from danger when he had to instead of going full inspector gadget (the show has two inspector gadget references) and solving his problems within a few seconds by pulverizing his enemies. Other than Rick's charecter detoriation, the show also acts condescending by breaking the "show don't tell rule" when the therapist confronts Rick that he was a Pickle in otder to avoid the therapy session. This episode made R&M from good to tollerable. "Rickdependence Spray" is bad because it is disgusting. The begining is dusgusting, the problem is disgusting, the solution for the problem is disgusting, and the end scene is disgusting. It is so disgusting that if I were to explain it I am sure that the moderators would give me a warning or more. Other than that this episode does not make sense because Rick, who had many "I told you so" moments towards Morty, somehow did not question Morty's blatant lies despite Morty acting suspicious whenever his cover is going to blow up.
The Simpsons also has a fair share of bad episodes (especially in the later seasons). Some notable examples include: Lisa Goes Gaga (Season 23): Probably the weakest guest star episode. It's literally just an advertisement Lady Gaga. The Principal And The Pauper (Season 9): This episode was so bad that even the creators declared it non-canon. It basically just says that Skinner is an imposter and the "real" skinner returns to call out the "fake Skinner". Thank god this isn't canon. Homer Vs. Dignity (Season 12): I don't really think I'm allowed to talk about this episode, but it literally features a scene where Homer is molested by a panda. The Boys Of Bummer (Season 18): This episode is very mean-spirited towards Bart, even though he only lost a baseball game. Bart also attempts to kill himself by throwing himself off a water tower, which is just too dark for The Simpsons. Also, this is just all my opinion, so it's okay to disagree.