Arthur makes fun of Sue Ellen's new sweater and insists her being offended is an overreaction, while in reality, he's being mean to her.
Tropes from "So Funny I Forgot to Laugh" include:
- Backhanded Apology: Once Mr. Ratburn gets word that Arthur is taunting Sue Ellen, he has him write an apology letter to her. Arthur does apologize in the letter, but also points out that he thinks that Sue Ellen is just overreacting. He does eventually give her a sincere apology at the end of the episode, however.
- Cyberbullying: Arthur sends Sue Ellen an E-mail showing her with a sheepdog's head, though he looks immediately regretful after sending it.
- Dude, Not Funny!: Arthur mocks Sue Ellen's new sweater. At first it's no harm but then he takes things too far to the to the point that nobody thinks that he is funny, instead they think he is mean. It even says it in the title itself.
- How We Got Here: The episode's Teaser has Sue Ellen writing an entry about her sweater in her diary before she writes about how mean people can be. Then after the title card, the events are shown in a flashback.
- Hypocrite: Francine and Muffy have made fun of others on various occasions in the past, yet are condemning Arthur for making fun of Sue Ellen.
- Hypocrite Has a Point: Undoubtedly Francine and Muffy were being hypocritical in calling out Arthur for being a bully considering that they're both not angels themselves but it's not like they were wrong considering how cruel Arthur was being to Sue Ellen throughout the episode to the point where the latter almost transferred classes.
- Innocently Insensitive: Arthur at first thinks he's just being funny and is surprised that Sue Ellen feels he's bullying her.
- Jerkass Ball: Arthur's bullying behavior toward Sue Ellen comes off as severely out of character, which Mr. Ratburn lampshades.
- Never My Fault: Arthur blames Sue Ellen for trying to get him in trouble, saying she should have just told him to stop. When Buster says that Sue Ellen did tell him to stop, Arthur says he didn't think she meant it.
- Out-of-Character Moment: All over the place:
- Arthur, usually a Nice Guy, is turned into a bully out of nowhere and keeps blaming Sue Ellen for being upset about it. Arthur of all people should know better, being a bullying victim himself.
- Francine and Muffy call Arthur out for being a bully, despite the fact that they themselves have repeatedly made fun of others, including Arthur.
- Sue Ellen is portrayed as unable to stand up for herself, when she's usually quick to confront people if they're being mean, and was shown to be able to intimidate Binky.
Arthur and his friends recall their favorite days ever.
Tropes from "The Best Day Ever" include:
- Bottle Episode: The whole episode takes place at the park.
- Clip Show: The episode shows many clips from previous episodes, though the voices from older seasons have been re-recorded.
- Flashback with the Other Darrin: The episode features clips from older episodes dubbed with the show's then-current voice actors.
- Once More, with Clarity: The episode adds a scene to the episode "Arthur's Dummy Disaster" which provides additional subtext for George's behavior; there's an aside with George hiding behind a shelf and trying to talk to and fix Wally before he runs outside and despairs over himself.
- Recap Episode: The episode features Arthur and his friends reflecting on their best and worst days.
