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.
There's also speculation that Frankie is an Imaginary Friend that Madame Foster made based on herself when she was younger.
Or similarly, that Madame Foster IS Frankie, time-traveled to the past.
Believe it or not, even Bendy is subject to this. Some people believe that his creator really did blame him for his own misdeeds, causing him toJump Off The Slippery Slope. This isn't entirely baseless; at the beginning, when his family's giving him up to Foster's, the kid is in the typical "I know I messed up and I'm ashamed" pose.
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.
Terrance, Mac's Big Brother Bully, isn't liked very much by the fandom either because he bullies Mac and he has no redeeming qualities whatsoever.
Eurotrish, primarily as an Ethnic Scrappy due to her design and constant off-key singing. She's also a rare In-Universe Scrappy since the people of Europe kicked her out of the continent for these reasons.
BLOO. Because of Bloo's strange change in character from being a snarky but still funny character to a complete Jerk Ass really left a sour taste in fans's mouth. As of 2014 (thanks to tumblr), many fans have started to dislike Bloo because of his rude, selfish, and egotistical personality, and to make it more insulting, he got worse as the show went on. Just look at the stream of nothing but negative traits on his character page. So many fans kept wondering as to why Mac didn't just ditch Bloo later on. And you know it's bad when the deuteragonist is loathed by the fandom and the other characters.
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".
They Wasted a Perfectly Good Plot: In the episode Foster's Go To Europe, anyone else like if they actually went to Europe? Imagine Bloo offending the locals and the wacky hijinks they'll pull across the continent.
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 inside 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 possibility that her parents aren't much help because they give her too much freedom and little to no guidance.