French Narrator (At the end of Nasty Patty): Well, that's our story. Yes, they are all idiots, aren't they?
Mr. Krabs and Spongebob catch wind of a fake health inspector being on the loose, while they have a health inspector of their own inside the building. You'd expect that Mr. Krabs would either send Spongebob out to ask the Inspector for legal documentation, if not do it himself. Instead they make the Nasty Patty.
Mr.Krabs has Spongebob make a nasty Krabby Patty. Just as the Inspector is about to take a bite, he chokes on a fly (underwater?) and passes out. Krabs later learns that the fake Health Inspector was captured. You'd then expect that Spongebob, Krabs, or someone else would go see if he's all right. He should still have a working pulse, and they could give him a real Krabby Patty and pass the inspection. Instead they think they've killed him, starting a long charade of burying him and hiding him from the cops, torturing (unintentionally) him in the process, even when he turned out OK.
"A Pal for Gary" is pretty much the definition of this trope. The whole episode involves Spongebob getting a new toy-like thing named Puffy Fluffy, for Gary to play with, completely unaware that it hates being around other pets (even when the pet seller told him that). He showers Puffy Fluffy with respect and tries to force Gary to accept him. That night, he thinks Gary and Puffy Fluffy will get along perfectly, but Puffy Fluffy transforms into a monster and terrorizes Gary throughout the house. It causes damage to Spongebob's house, and the next morning when Spongebob wakes up, he thinks Gary is responsible! He enters the living room and sees Gary in Puffy Fluffy's mouth! You'd expect that Spongebob would try to save Gary. Instead he angrily tells Gary to put Puffy Fluffy down. Uh, yeah, he can't do that right now, because Puffy Fluffy has him IN HIS MOUTH! As he continues to rant, he is then taken by Puffy Fluffy's fangs.
Then, Gary saves Spongebob by using a lasso and acting like a cowboy, and knocks Spongebob out of Puffy Fluffy's mouth. Puffy Fluffy then breaks out of the pineapple house and flees. You'd then expect that Spongebob would finally realize what Fluffy really was, and apologize to Gary for treating him so terribly, considering he, oh you know, JUST SAVED HIS LIFE. Instead he tries to get Puffy Fluffy back, but after that fails, he scolds Gary AGAIN. WHAT?! He neglected his own pet horribly in favor of a monster and NEVER apologized! And despite that, they make up in the very next scene with little trouble, in which Spongebob decides to take Gary to work everyday so he won't neglect him. Extra idiot points: Considering that at the beginning of the episode, Spongebob felt bad and that he was neglecting Gary, he should have thought of THAT while Puffy Fluffy was there, but NOOOOOOO. Let's just face it: Spongebob was more of a jerk than usual in this episode.
A basic staple, Spongebob going to Patrick for advice. You'd expect that Spongebob would realized that Patrick is Too Dumb to Live. Instead the situation goes From Bad to Worse.
In "The Slumber Party", SpongeBob uses a pizza man disguise to get inside Pearl's party for survelliance, forced to do so by Mr. Krabs. The mustache flies away and Pearl and her friends confront SpongeBob. SpongeBob runs to Mr. Krabs and tells him to "STEP ON IT!!!" so that way he doesn't get maimed. You'd expect that Mr. Krabs grabs SpongeBob and drives him home. Instead he takes the "STEP ON IT!!!" term too seriously and drives off without him. And that ultimately causesSpongeBob get impounded into a pizza, and he ships himself to Mr. Krabs. You'd then expect: Wait, it's been shown that SpongeBob can change into different shapes, so couldn't Mr. Krabs do something to revert him back to normal? Instead: He takes a piece of SpongeBob, eats it, complains that he's cold, tells him that he should've been here earlier (this is coming from the guy that drove away from him and left him in danger), and takes another slice of SpongeBob!
In "Shellback Shenanigans", Plankton disguises himself as Gary, SpongeBob's pet snail, to get the Krabby Patty formula. You'd expect that SpongeBob realizes that so-called Gary that's "turning green and talking" is really Plankton. Instead he actually believes that Plankton is Gary. Not only that, the doctors (who are PROFESSIONALS) thought he was Gary, too!
In "It's a SpongeBob Christmas!", Plankton decides that in order to get the Krabby Patty, he needs to sell fruitcakes with the fake element "Jerktonium" in them. He goes to sell it and finds SpongeBob, who eats all of the fruitcake without turning into a jerk. When Plankton walks off, SpongeBob sells the food to nearby Christmas carolers, who turn into jerks upon eating them. You'd expect that SpongeBob realizes that the fruitcake has Jerktonium and tries to get rid of it. Instead, since he's immune to Jerktonium, he goes around selling the fruitcake—and promptly turns everyone into jerks!
In "No Free Rides," Mrs. Puff gives extra credit and passes Spongebob so she doesn't have to deal with him for another year. Spongebob ends up getting a boatmobile from his parents. You'd Expect That Mrs. Puff would explain to Spongebob about what she did in order to guarantee that he won't wreck havoc with his bad driving. Instead She attempts, and fails, to steal his boatmobile and ends up landing herself in jail.
In One Coarse Meal, after being horrified to no end by Mr. Krabs and almost committing suicide, Plankton gets told a secret by Spongebob: Krabs is afraid of mimes. So Plankton does this to get back at Mr. Krabs for terrorizing him by bringing a mime over. You'd Expect: That Plankton goes back home after this, happy to finally having gotten revenge. Instead: Spongebob drives him back home screaming at seeing (holographic) whales nearby. And Mr. Krabs congratulates him for it. Thus: Mr. Krabs is a Karma Houdini.
In The Movie, when Squidward confronts Plankton at the Chum Bucket. You'd Expect: For Squidward to keep his mouth closed and not reveal to Plankton that he knows his plan, and notify the authorities when he leaves the Chum Bucket right away. Instead:He explicitly tells Plankton about his plan and says that he will report him, thus allowing Plankton to activate the Chum Bucket helmets and the mind-controlled citizens kidnapping him.
In "Little Yellow Book", where Squidward catches SpongeBob writing in his diary and when Squidward has it in his hands, wondering what it is, SpongeBob Defensively takes it away from him. You'd Expect: SpongeBob would keep it with him or hide it when Squidward's not around. Instead: He leaves it out in the open and Squidward reads it after luring him away. Thus: SpongeBob is humiliated. But Then: He publishes the diary because it made people laugh, completely forgetting that it was that thing that humiliated him. Extra Idiot Points: He tells Squidward that he has an even more embarrassing diary and even shows it to him. And That Ultimately Causes: Squidward takes and reads that diary while his back is turned, humiliating him once again. Just, wow. So Basically: SpongeBob is clearly unfit to keep a diary if he can't protect it from nosy intruders. Why Do We Even Bother:Spongebob doesn't even think about the way Squidward treats him in this episode, and acts nice to him. But, of course this is Spongebob we're talking about, so why should we even be surprised.