Bart is inspired by one of the school's motivational speakers to become a cartoonist, in which he creates a popular comic and later internet series titled "Angry Dad", which is based on Homer's anger problems. Homer becomes the town's laughing stock, and decides to give up anger completely.
At Springfield Elementary School, Kirk Van Houten holds an unsuccessful short speech about his occupation of being an assistant flyer distributor. Principal Skinner becomes disappointed about not being to find any good speakers for their assemblies about the importance of studying. In his office, Lisa points out the reason that none of the students are following the "buckle down and study" protocol is because the faculty is letting anyone speak, using Mr. Van Houten, Groundskeeper Willie and his enemy, Shamus as prime examples since their encouragement is poor. She suggests that they head to the Hall of Motivational Speakers to find someone who can motivate the students at Springfield Elementary to study more.
There, Lisa suggests they bring in cartoonist Geoff Jenkins, the creator of a cartoon named "Danger Dog" to motivate them. At the next assembly, Geoff tells the kids how easy and rewarding his job is and that he didn't even need to work hard in school to get it, and all he does is "eat candy and watch R-rated movies". This infuriates Skinner because he isn't encouraging the students to follow the "buckle down and study" protocol and pulls the fire alarm in an attempt to distract them. Once they are out of the auditorium, he confronts Jenkins for his behavior and promptly kicks him out. Jenkins' speech prompt all the students to start stop paying attention in class and try to become cartoonists.
However, their creativity is sadly lacking and they all create blatant rip offs of "Danger Dog", especially Bart, who makes the worst rip off called "Danger Dude", which turns out to be a dog. Expecting to make millions, he shows his work to Comic Book Guy, who, with no mercy, criticizes his comic as the worst comic he has ever seen. Stan Lee enters the store and judges Bart's comic. Lee agrees with Comic Book Guy, but encourages Bart to keep trying. Bart then sits at home, struggling to think of a new idea for his comic, notices an angry Homer outside trying to unfold a lawnchair. Bart then spawns the idea of making a comic about Homer's anger problem, thus creating the comic "Angry Dad".
The next day, Homer catches Bart drawing him and thinks he's doing it because he hero worships him. Losing his temper at an intersection for making him wait, Bart is further inspired. He publishes the first issue of Angry Dad, making an instant hit at the kids at school. Having read the issue, Lisa hates it and confronts Bart by calling him out for his obvious plagiarism of Homer's activities. She thinks it's insulting for him to poke fun at their father because of his anger management issues. Bart calmly claims he will add a new character to the series called Know-It-All Sister (based on her) as Angry Dad's new sidekick. Lisa reconsiders as long as she gets a pony and the last line of each scene.
Later, Bart shows Comic Book Guy his new and original comic, and Comic Book Guy likes the comic and dubs it as "shelf worthy". Bart notices Stan Lee across the room, trying to persuade Database that a "Thing" action figure from the "Fantastic Four" fits perfectly in his toy Batmobile, but ends up breaking it. Bart asks why Stan Lee came back, when Comic Book Guy remarks "Stan Lee never left. I'm starting to think his mind is no longer in mint condition". Bart later hosts an autograph signing session in the schoolyard, when a spokesperson from an Internet company titled BetterThanTV.com wants to make Bart's comic into an online animated cartoon series. Bart agrees as long as he gets his share of stock.
"Angry Dad" then becomes the single most popular non-pornographic website of all time, making it 10 trillionth overall. The only one still unaware of it, ironically, is the inspiration of the series, Homer. He soon learns the truth when he finds Lenny, Carl, Smithers and Mr. Burns watching a webisode in which Angry Dad's head explodes after reading a headline in the newspaper that reads "YOU SUCK, ANGRY DAD!". At first, Homer finds it amusing until he took notice of the similarities between him and Angry Dad. Infuriated at Bart for making him a world-wide laughingstock in Springfield, Homer rushes home to strangle him. During the ride back, several residents recognize him and do their best to make him angrier. Despite Homer's warning not to make him more angry than he already is, the townspeople succeed resulting his hand getting stuck in one of the car door and giving him pain, followed by Moe stealing Homer's car and crashing it into a streetlight, causing it to be set on fire. They laugh at him more as he rushes home to confront Bart.
Once the humiliated Homer comes home, he catches Bart and Milhouse laughing at another Angry Dad cartoon. He attempts to strangle him, but the family stops him just in time. Lisa and Marge points out that he has problems controlling his anger, even showing Homer that he's punching the cat without even realizing it. Homer finally admits to having anger management issues and he couldn't help it when he's enraged. Lisa admits while she's not a fan of Bart's cartoon, she suggests he tries to work on his anger problems. Homer agrees to address them and be more calmer by suppressing his rage as much as he can. When Marge insists he goes on a diet while dealing with his anger issues, Homer rebuffs her request, claiming he will only give up anger and not his favorite foods.
Homer then starts to take a walk outside when he realizes that a lot more things anger him then he thought, such as the paper boy, the milk man, and the piano lady throwing their respective objects at him, discovering that Marge invited Ned Flanders over to have a sing-along, and the town of Springfield trying to egg Homer on to do something angry. In spite of that, he stills keeps his promise and holds back his rage. This however, cause lumps to break out on Homer's neck everytime he suppresses his anger, which he forces down.
Bart starts to run out of ideas for "Angry Dad" sketches after Homer's promise to stay calm, so Bart and Milhouse come up with a trap for Homer in order to infuriate him. It becomes too late when the internet company goes bankrupt. He soon realizes that he no longer needs the trap he set up, and rushes home to dismantle it. Homer reaches home when he notices a "Free Doughnuts" sign on the front door leading to Bart's treehouse. Homer climbs up in order to get his doughnuts, when he falls through a carpet-covered hole in the floor and gets hung upside-down by the foot dangling from a laundry line, which starts to move. He passes through a placed set of cacti and dirty diapers, and reaches the end of the line where he finds scissors to cut him down, and falls into a kiddie pool filled with green paint. Homer is now covered with green and resembles The Incredible Hulk, and
releases his pent up rage through a rampage across town. The police then easily restrain him as he is not as strong as he appears to be. Stan Lee is seen at the sidelines, ranting how he is actually The Incredible Hulk. Lee then miserably fails at trying to transform in The Hulk, as Comic Book Guy remarks that he "couldn't even transform into Bill Bixby" and how he wishes that he could have the power to leave his store.
Later Homer is admitted to the hospital, where an infuriated Marge berates Bart for aggravating him and $10 million in damages for his prank. She promises to punish him for it and this makes Bart feel guilty for it. However, Dr. Hibbert arrives and disagrees with Marge by stating that Bart actually saved Homer's life by enraging him. He points out the boils on his neck were caused by his suppression of rage which would've overwhelmed Homer's nervous system had Bart's prank not set him off with the violent outburst. Dr. Hibbert convinces a reluctant Marge to go easy on him. Homer decides to stop getting angry and Bart decides to stop making Angry Dad cartoons. The two then go fishing where Bart still angers Homer, which he is thankful for.