Big Fat Liar

Jason Shepherd is a 14-year-old compulsive liar living in the town of Greenbury, Michigan, who tries to lie his way out of failing to write a creative writing assignment. He gets caught by his English teacher, Ms. Caldwell, and is given three hours to submit his essay and avoid repeating English in summer school. Remembering a comment from his father about making up stories being his “God-given talent”, he writes a story titled “Big Fat Liar”, drawing inspiration from his lying.
While riding his sister's old bike to turn in the essay (after a bully stole his skateboard earlier), Jason is accidentally struck by a limousine driven by Marty Wolf, an arrogant and unscrupulous Hollywood producer whom Jason blackmails into giving him a ride. Marty, a pathological liar, is in town shooting his next film, Whitaker and Fowl. In a rush, Jason accidentally leaves his essay in the limo when it falls out of his backpack. Inspired, Marty keeps the story for himself. After discovering his essay is missing, Jason is sent to summer school for failing to convince his parents and Ms. Caldwell that it was left in Marty's limo.
During the summer, Jason and his friend Kaylee go to the movies together, where a teaser trailer for Big Fat Liar is shown. After failing to convince Jason's parents of the truth, they fly to L.A. while their parents are out of town for the weekend and sneak into Marty's studio office. Jason demands that Marty confess to his parents, but he refuses, purposefully burns his essay, and calls security to remove him. Angered, the teens plot to inconvenience Marty until he confesses, and Marty's former limo driver and struggling actor Frank Jackson agrees to help.
Jason and Kaylee sabotage Marty through pranks such as dyeing his skin blue via his swimming pool and his hair orange via his shampoo. They also superglue his headset to his ear, trick him into attending a child's birthday party, where the children mistake him for the hired clown and attack him, and tamper with his car's controls, causing it to malfunction. Additionally, Marty accidentally hits a monster truck driver when an elderly woman, whom he had insulted earlier, rear ends him. The Monster truck driver, thinking Marty purposely hit him, runs over and crushes Marty’s car. These pranks and the incident with the monster truck driver cause Marty to miss both of his appointments with Universal Pictures president Marcus Duncan. Seeing the commercial and critical failure of Whitaker and Fowl, Marcus threatens to shut down production on Big Fat Liar. Jason offers to help Marty in exchange for his confession to his parents. During a party at Marty's house following the premiere of Whitaker and Fowl, Wolf uses Jason's advice to deliver a successful presentation and secure Marcus's approval of the film. Marty reneges on his deal with Jason and calls security to have him and Kaylee removed again. Fed up with his abuse, Marty's assistant and aspiring producer Monty Kirkham offers to help them expose him, rallying Marty's other tormented employees, while Jason calls his parents to tell them the truth about the weekend.
The next morning, Marty heads to the studio to begin filming Big Fat Liar, but his employees delay him through many mishaps. As he finally arrives, he encounters Jason, who steals his stuffed monkey toy, Mr. Funnybones. Jason flees across the studio with Kaylee's help, luring Marty to a rooftop where he retrieves his toy and mocks Jason. Marty boasts of his actions, falsely believing that no one is listening (or ever will, refusing to tell the truth, believing it to be "overrated"), unaware that the entire conversation is being broadcast to Jason's parents, the media, and Marcus, who immediately fires him for dishonesty and plagiarism. Furious, Marty tries to attack Jason, but the latter leaps from the building and lands safely on a stunt cushion, where he reunites with his parents, now aware that he was telling the truth and that he did all this to prove it.
Universal produces Big Fat Liar with the talents of those whom Marty mistreated, including Monty as writer and producer, and Frank as the lead character, Kenny Trooper. Jason receives full credit for his story, and the film becomes a success, as his parents and Ms. Caldwell are proud of him. Marty now works as a birthday clown named "Wolfie the Clown". His first job is at a house where a boy named Darren lives. Unfortunately for him, Darren's father, the Masher, as retribution for Marty having previously damaged his truck, has Darren drop-kick Marty in the groin.