The Simpsons live in a heightened cartoon world, where the residents of Springfield will often act in comically exaggerated ways, but there is a limit to how far the town can go, with one notable episode pushing Bart Simpson to the absolute brink. Season 18, Episode 18, "The Boys of Bummer," features one of Springfield's lowest points as the town almost breaks Bart's spirit.
"The Boys of Bummer" focuses on Bart's little league career with the Isotots. The team reaches the championship game against Shelbyville, but Bart costs Springfield a victory on an unforced error. The entire town becomes increasingly bitter and furious with Bart as a result, leading the ten-year-old boy to become something of a pariah. The local radio mocks him, Chief Wiggum won't protect Bart from abuse, and even Lisa's attempts to cheer him up by introducing Bart to a former baseball player leads to more attacks against Bart.
Eventually, the non-stop insults push Bart too far, leading him to have a minor breakdown. Bart moves throughout the entire town and spray paints, "I HATE BART SIMPSON," on every surface he can find. Eventually climbing to the top of the local water tower, Bart tells the assembled town that he hates Bart just as much as they do, and now they can all go back to treating him as just another member of the town. Marge demands the town apologize for their actions, but the town refuses, with Chief Wiggum even shouting at Bart to jump. Bart does just this, crashing into the ground and getting injured.
However, even this doesn't break the town's scorn for Bart. As he recovers in bed, the denizens of Springfield gather outside the hospital to boo Bart, even creating signs and banners to further taunt him. This turns Marge fully against Springfield, leading her to insult the entire town and condemn them for their treatment of her son, ultimately declaring Springfield to be the meanest city in America. This finally gets through to the town, who sheepishly apologize to Bart and try to stage a new game to make him feel better.
Springfield is frequently shown throughout the series to be known primarily for its more violent and unpredictable side. Episodes like Season 6, Episode 18, "A Star Is Burns," and Season 16, Episode 10, "There's Something About Marrying," highlight that the rest of the country considers Springfield to be a needlessly cruel town.
Even the citizens' tendency to form angry mobs and riot make Springfield one of the best examples of how quickly hate can overtake people and lead to destruction. The residents don't even try to cover up their crimes much of the time, flaunting their ill-gotten gains after rioting in Season 13, Episode 22, "Poppa's Got A Brand New Badge."
The town is often shameless in its cruelty and lack of protections for the citizenry, but "The Boys of Bummer" takes Springfield to a new level, with any justifiable dislike for Bart and his antics being overshadowed by how cruel the town treats the kid. As Marge has to forcibly remind the entire town, Bart is just a child and will be traumatized by the events of the episode. The fact that the town doesn't even unite around Bart after his injury speaks to the selfish and short-sighted nature of the town. It's the worst impulses of the nominally average citizens, and they fully embrace that darker side.
"The Boys of Bummer" is a notably controversial episode within The Simpsons fanbase, with some appreciating the ridiculous nature of the town's rage while others have railed against the town and consider it to be among the worst depictions of Springfield in the entire series. At the end of the day, this is an episode where a town of capable adults took out their rage against a child for a mistake he made during a local little league game. For a town so well-conditioned to lose -- with multiple gags being made about how Springfield has never won any major sports competition -- it's a brutal amount of mental abuse on a kid, and it's easily Springfield's lowest moment as a town.