The titular character of Bojack Horseman got his big break as the star of a 1990s sitcom (an Expy of Full House), and seems to be convinced that things will all work out in the end after some solemn speeches. The universe is all too happy to prove him wrong about this, time and time again. In the first season's finale, Bojack apologizes to his old friend Herb for choosing the spot in the sitcom over his friendship with Herb years ago. Not only does Herb not forgive Bojack, he rips into Bojack with a "The Reason You Suck" Speech.
An In-Universe case happens in Drawn Together. Captain Hero spends much of the first episode thinking that the reality show he and the other housemates are on is one in which the contestants vote each other out and the last one standing receives a prize; as such, if Clara succeeds in ejecting Foxxy, he will be one step closer to victory. Foxxy tries, in vain, to convince him that it's not that kind of reality show.
In "Homer Goes to College", Homer is convinced that college is nonstop Wacky Fratboy Hijinx a la Animal House and Revenge of the Nerds, which includes believing Dean Peterson of Springfield University is a Dean Bitterman type (the same episode doubling as the introduction of the original Dean Bitterman) and spends most of the episode pulling ill-conceived pranks on him, even going as far as to try to run him over with a car at one point. The irony is that Peterson is actually a good-natured younger guy who gets on well with the other students. And when he tries to pull a prank, his nerd classmates get expelled when they're caught.
Bart has a similar experience in "The Town". When the family decides to move to Boston, Bart is ecstatic, convinced he'll soon be working up the ranks of the Irish Mob. Unfortunately, he soon finds out the city is actually a gentrified, intellectual paradise rather than the working class gangsterland it's depicted as in The Departed and The Town.
"Das Bus", when the entire class gets stranded on an island, Bart is convinced that this is a castaway story like The Swiss Family Robinson. Sadly for him, they're actually in Lord of the Flies which isn't like that.note It really, really, isn't.
SpongeBob SquarePants: In "Krab-Borg", SpongeBob becomes convinced that Mr. Krabs is a robot thanks to having seen a movie where robots take over the Earth (and some coincidentally odd behavior on Mr. Krabs' part). After he and Squidward have ruthlessly interrogated the "robot", Squidward thinks to ask SpongeBob how the movie ended, to which he replies that it turned out there weren't any robots after all; it was a misunderstanding. Oops.
In a few episodes of Teenage Mutant Ninja Turtles (2003), Michelangelo loves monster movies and panics when he meets creatures from beneath the earth, body-snatching aliens, or eldritch horrors. Someone always dies horribly. Lucky for him, he's not in a monster movie — he's in a Saturday Morning Cartoon.
Transformers Prime episode "Thirst" has Starscream and Knockout confronted by a Terrorcon, and Knockout suggests shooting in the head based on seeing human horror films, citing tactics for killing zombies. Except this isn't a human horror film. And depiction wise, the Terrorcons in this episode are more like vampires. Both of these lead to his plan failing.
Wander over Yonder episode "The Hero" has Brad Starlight who claims to be the hero of a fairy tale and is out to save the princess from an evil dragon king and is destined to marry her. He's actually her Stalker With a Crush who can't accept no for an answer and is under the delusion that he's a hero. He thinks Wander, the real hero, is his goofy sidekick, Sylvia, Wander's partner, is a dumb beast he uses as his steed, and the competent princess who genuinely loves the dragon king is a Damsel in Distress being help captive. He tries to kidnap her, refusing to admit he was wrong, and she subsequently kicks his hide.
Wunschpunsch: In an attempt to prevent Bubonic and Tyrannia from casting the spell of the week in "Plant Panic", Maurizio places some banana peels to make them trip and believes the plan would work because he's seen it happening in cartoons. They simply walk normally and are oblivious to the banana peels despite having stepped on some. Maurizio later falls for his own trap. Just like it happens in some cartoons (and other media sometimes).