Bart-Mangled Banner is the twenty-first episode of Season 15, which first aired on May 16, 2004. The episode was written by John Frink and directed by Steven Dean Moore. An accidental photo showing Bart "mooning" the American flag makes the Simpsons the most hated family in town.
Homer and Marge take the kids to get their shots. Just before Dr. Hibbert is about to inject Bart, he escapes. After a chase through town, Hibbert finally outsmarts Bart by having Barney and Moe impersonate him and the real Hibbert injects Bart. The shot, however, causes Bart's earholes to swell shut, making him temporarily deaf. Hibbert also tricks Homer into signing a malpractice waiver.
While at the Springfield Elementary School donkey basketball game, Bart taunts a donkey with a carrot, unaware that the school is reciting the National Anthem. After he places the carrot in his shorts, the donkey takes it and rips off Bart's shorts (just like his famous line "Eat my shorts") thus exposing his bare buttocks. While Bart is bent over to keep his privates covered with his shirt, the US flag is put up behind him and a photo is taken, which results in the crowd assuming that Bart is mooning the US flag. Shortly afterwards, The Springfield Shopper takes the story and completely turns it around, making it seem as if Bart had deliberately mooned the flag. He and his family soon are hated by all of Springfield. Homer and Marge tried to clear up this misunderstanding, knowing that it was an accident, but everybody refuses to listen, mistrusting Bart and his family.
The Simpsons are later asked to appear on a talk show and tell their side of the story. However, the host asks, instead, "What part of America do you hate most?" (an example of the fallacy of many questions). Marge says that, if leading questions such as that are the only forms of discussion in America, then she does hate America. She also said that she is well-liked in Springfield, prompting the host to say that Springfield hates America. The US then turns their back on Springfield, so Mayor Quimby frantically decides to change the name of Springfield to "Libertyville." Everything in town is quickly patriotized; the traffic light colors are changed to red, white, and blue, and everything costs $17.76. While at church, Lisa speaks her opinion about patriotism, and the Simpsons are taken into custody, in violation of the "Government Knows Best Act".
The Simpsons are taken to the "Ronald Reagan Reeducation Center", which houses Michael Moore, the Dixie Chicks, Elmo (who accidentally went to the wrong fundraiser), and Bill Clinton. With some help from the last-registered Democrat, the Simpsons escape the prison, but realize that the re-education center is actually Alcatraz Prison. While they are swimming to land, they are picked up by a French freighter and are brought to France. They are well adjusted, but still miss America, mainly because it is where all their stuff is. They then move back to the US dressed as 19th century immigrants from Europe where Homer speaks of plans of integration into America.