Principal Skinner and Mrs. Krabappel take Lisa's advice and visit the Springfield Writer's Forum to find a better speaker. They find Jeff Jenkins, creator of a popular TV cartoon, Danger Dog. He comes to the school to give a presentation on Danger Dog, including showing them a sneak preview for the next Easter special, and fascinates the kids by telling them about the cartoon industry. Much to Skinner's horror, Jenkins tells the students how easy his job is and how he never needed to work hard to get his job. Panicking, Skinner pulls the fire alarm and interrupts the speech, hoping to keep the students from absorbing Jenkins lazy attitude. Unfortunately, every kid in school creates their own comic book, all of which are actually rip-off versions of Danger Dog. Bart also creates his own comic Danger Dude (which is actually a dog) and tries to sell it to Comic Book Guy, who criticizes his work. Stan Lee enters Comic Book Guy's store and tells Bart that his comic is bad. However, he encourages Bart to keep trying to "find his own voice".
At home, Bart comes up with a character called Angry Dad, based on Homer and his frequent outbursts when he does something stupid. Bart rolls out the first issue of Angry Dad, which becomes a hit with the kids in school. However, Lisa points out that the character is a carbon copy of Homer. Bart responds by deciding to make a supporting character for Angry Dad: a character named Know-it-All Sister based on Lisa's annoying yet wise personality. Soon, Lisa relents as long she gets a pony and the last line of the comic, allowing Bart to make more issues of Angry Dad. Upon reading Angry Dad comics, Comic Book Guy deems them impressive enough to sell, much to Bart's delight.
During an autograph signing session in the schoolyard, Bart is approached by a spokesman for an Internet entertainment site. He wants to make Angry Dad into an online animated cartoon series, and Bart agrees in exchange for stock. The cartoon becomes an Internet hit, becoming the single most popular non-pornographic website of all time, which according to Lenny makes it "tenth trillionth" overall. The only one still unaware of Angry Dad is Homer, who finds out one day at work when Lenny, Carl, Smithers, and Mr. Burns find it hilarious. At first, Homer finds it very funny, but learns that he looks exactly like Angry Dad and that Bart is the one who created it, much to his anger. He becomes a laughingstock both on the web and in Springfield. While driving home, the humiliated Homer is stopped by various townsfolk, who do what they can to make him all the more angry. As a result, he carelessly slams the car door on his own hand, causing him immense pain. The townspeople respond with even more jubilance as the humiliated Homer flees towards home. Once he arrives, the apoplectic Homer finds Bart and Milhouse laughing at a new Angry Dad cartoon. He strangles Bart for the humiliation the town has given to him through his cartoons. Eventually, Marge and Lisa stop Homer and manage to calm him down. Though Lisa admits to not being a fan of Bart's comic, she does tell Homer to address his anger management issues once and for all. Homer agrees to try to tame his anger from that point on. However, he refuses Marge's request to go on a diet while he is dealing with his anger issues.
The next day, Homer stays true to his word and remains calm, despite having difficulty maintaining it, as it is evident that whenever aggravating situations occur, Homer tries to suppress his rage, causing lumps to grow on his neck. However, his new calm demeanor has taken away Bart's inspiration for his cartoon, so Bart and Milhouse set up a prank for Homer to trigger another outburst. Later, they go to the Internet company office, where they find the company has gone bankrupt, due to its poor financial model and devalued stock. Realizing that this means he doesn't need more material for Angry Dad, Bart and Milhouse rushes back to the house to defuse the trap. Homer reaches home and happens upon Bart's trap, but he keeps his calm throughout its run, causing more lumps to develop on his neck. The trap ends with Homer falling into a pool full of green paint and resembling the Incredible Hulk, finally prompting him to go berserk and storm through town, causing much damage. The police restrain him and Homer is admitted to the hospital.
At the hospital, Marge tells Bart she is disappointed in him for aggravating Homer's rage with his prank, because of the $10 million in damages his father has caused with his rage, and she mentions that when they get home, she will punish him for it. However, Dr. Hibbert arrives and disagrees with Marge by telling her that Bart actually saved Homer's life by enraging him. He explains the lumps on his neck were actually boils caused by suppressed rage and would have otherwise overwhelmed his nervous system if Bart's prank had not set him off. Hibbert convinces a reluctant Marge that she should go easy on her son for it. Homer thanks Bart by taking him fishing, where he continues to make his father angry, though this time, Homer tries to control it for good.