These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Foster's Home for Imaginary Friends
Accidental Innuendo: When Mac, Bloo, and Cheese are building their go-cart, Bloo mentions about Cheese screwing everything up. How does Cheese respond? "Nuh-uh, I'm only screwing the wheel!"
Also, Bloo. Some fans find him very entertaining and endearing because of his antics, while other fans find him as an obnoxious jerkass who doesn't deserve Mac as a friend.
Broken Base: The show's attempts at Black Comedy and/or Kafka Komedy ("Foster's Goes to Europe", "I Only Have Surprise For You", "Imposter's Home For Um... Make Em Up Pals," etc...) usually resulted in this.
Canon Fodder: Wilt. His Backstory wasn't revealed until the special "Good Wilt Hunting", spawning many, manyFanfics that provided their own explanation for his scars and history, often treading into Darker and Edgier territory than the actual series.
Crazy Awesome: Madame Foster. Worried you'll get in trouble for starting a party in the house? You sure will for not having her along.
Case in point, she's left to deal with a bear. Next time we see her she's riding the bear naked!
Cheese became this for many fans. Ironically, the reason Cheese became a Creator's Pet is because he was immensely popular with the fans in his debut episode. You know what they say; there is such a thing as too much, er, cheese.
Bloo also started to become this for a few fans after a while.
Crowning Moment of Heartwarming: Mr. Herriman. Near the end of Destination: Imagination, when he admits that he was wrong about Frankie and finally shows her some respect, even trusting her judgment in opening the box containing World. For long-time fans who are familiar with the characters, it's especially touching.
"Funny Aneurysm" Moment: The scene where Wilt freaks out some kids by pulling a fake arm off his nub arm is pretty funny the first time through. Once we learn his backstory though ( speciffically that he had to get the arm amputated after it was crushed beyond repair.) it becomes much darker. Not to mention a rather dark instance of Foreshadowing.
Hilarious in Hindsight: "World Wide Wabbit", which sees footage of Mr. Herriman's dancing for Madame Foster being uploaded to the internet, seems to be a spoof of YouTube Poops... until you realise that the episode premiered before YouTube even existed.
Seasonal Rot: Many people like to pretend everything after season 1 never existed despite the latter seasons introducing new characters with great personalities and giving some characters more depth, though Bloo's Flanderization may have something to do with it.
Suspiciously Similar Song: During Bloo's movie, Wilt performs a song that sounds very similar to "All Star" by Smash Mouth. Including the words "Hey Now".
Villain Decay: Duchess. She was really only a villainous character in the pilot. After that she just became snobby and apathetic to everyone around her.
World, the reality-changing friend inside the toy box's imaginary world in Destination Imagination, is probably the biggest woobie in the series. The majority of the events in the special happened because of his emotional instability.
Which only existed because he'd been locked up intside a trunk by his creator's parents for an extremely long time, where he could create absolutely anything he wanted...except other sentient beings to share it with. No wonder the little guy was an emotional timebomb.
To a certain extent, Goo, at least in her debut episode. Prior to meeting Mac, she had no human friends and created imaginary friends to keep her company. It's even a bit worse in hindsight because when she tells this to Mac, she says nobody likes her because she's a "big, fat weirdo", subtly implying she might have been bullied before. There's also the possiblity that her parents aren't much help because they give her too much freedom and little to no guidance.