Barthood

"Barthood" is the 9th episode of season 27. It aired on December 13, 2015.

Past
The episode begins with Homer and a 6 year old Bart laying down on the grass, as Bart asks things about nature to his father, only for Homer to ask him why did he leave his toy cars on the stairs, resulting in many injuries for him. The family decides to take Bart to Abe's house to take him away from Homer. As Bart asks grandpa to play with toy cars, he remembers about an old Studebaker Starliner Commander he had bought brand new in 1954 and forgotten about. Bart asks if he can sit on it, but grandpa reveals that Bart can actually drive it.

The episode fast-forwards 2 years to the future, with Bart still driving grandpa's car, late for his reading class. Jonathan Frink tries to teach him without much success, and discovers that Lisa, who's 2 years younger can read almost perfectly. Later, Lisa paints a boat on the sea, to which Marge replies they're placing it over the couch. That's when Bart reveals that he made a painting on the entire kitchen. While Homer is painting the walls and furniture to its original color, Bart tries to impress Lisa by driving Homer's car, only to crash it through the kitchen wall, almost hitting his father.

Homer and Marge decide to go to a psychologist to see why their son is such a troublemaker. She says that it's because of Homer's lack of attention for him and that they should go camping together. But instead of taking the boy to camping, Homer takes him to an inn only for him to watch a game, making Bart sad. Back at home, he discovers that Lisa is the student of the month at Springfield Elementary, even though she has been in the school only for a month, while Bart has been there for two years and haven't won anything. Homer tries to reconcile with him by saying he loves both of them the same amount: 40%. Bart makes a bumper sticker for Homer's car, but he ignores it because there's no more space for stickers in his bumper.

Future
The episode fast-forwards to Bart's 12th birthday, where Lisa gets the news she's student of the month at Springfield Elementary for 48 consecutive months. Bart gets angry because his sister can overshadow him even at his birthday party, so he decides to go skateboarding with Milhouse. They decide to break street lamps, but Milhouse gets arrested and taken to juvie while Bart was hiding at the Retirement Castle, where Grandpa gives him a BMX bike.

Three years later, Bart is good at making stunts with his bike and Marge and Lisa go on a camp together, leaving Homer and Bart alone. Marge mentions that this could be Homer's last chance to have a close relationship with Bart, only for them to talk a few seconds and Homer leave him home alone once again. Bart throws a party at their home, and it is shown that Bart has a relationship with Terri, but it was actually Sherri, as stating "You make out just as good as Terri said you did." Bart later finds Homer and Wiggum high on pot, where he reveals that he was exactly like Bart, but when he was born, this meant he was not a kid anymore. They hug each other, but their moment is ruined when Homer mentions that he will not go anywhere or do anything.

Bart goes to Grampa's grave, where he gets the idea of going to a BMX competition, where he would never be overshadowed by Lisa. At one of his stunts, however, he gets distracted by Lisa's shadow, hits the ground too hard and blacks out, only to discover that he was brought back to life by Lisa who's now proclaimed as a hero, making him angry. Bart decides to make caricatures at the port, where he's invited to Milhouse's graduation party. He's reluctant to go because his sister is graduating the same year as them, but he decides to go anyway.

At the party, Milhouse's parents fight in front of him, so Lisa tries to make him happy by saying he's "cuter then ever", resulting on Milhouse replying that she's the best thing at that party. Bart gets irate that he's always the second best Simpson in everything, but Lisa confronts him by saying she's tired of him blaming her for every setback in his life, and that he's a good artist, even though he never does anything with his talent. Bart decides to take his sister's rage as advice.

Two years later, Bart opens a bike customization shop, where he's surprised by Nelson, who wants to give all the lunch money he stole at school back, giving Bart $5.000. He's also surprised to see that Lisa and Nelson are dating (again). He shows them a giant painting on a wall, showing various moments through his life. Lisa realizes that she's not on any part of the painting, so Bart lower one of the shop's doors to show her a giant painting made in her homage as one of his favorite sisters. The episode ends with Nelson discovering that El Barto is actually Bart.