The episode starts out with SpongeBob waking up and singing the song, "Best Day Ever," and he describes to Gary what he plans to do on this day: do his "perfect" job at the Krusty Krab, practice karate with Sandy, go jellyfishing with Patrick using his new high-tech net, and at the end of the day attend Squidward's big clarinet recital. However, SpongeBob's "Best Day Ever" does not turn out as he plans. He goes to the Krusty Krab, only to find it condemned due to a severe nematode infestation. He then tells the nematodes to leave, but they eat his pants instead. SpongeBob begins playing the "Best Day Ever" song with his nose, causing the nematodes to follow him. Mr. Krabs tells SpongeBob to keep playing and lead them as far away as possible, and he does so until they all fall asleep (including SpongeBob).
He then goes to Sandy's tree dome for karate, but Sandy is busy trying to fix a leak in the roof of her treedome. SpongeBob thinks that this is a trap, and attacks her anyway. Sandy hits him and sends him flying up to the roof, and his glove sticks to it, sealing the leak. Afterward, SpongeBob heads over to Jellyfish Fields to go jelly fishing with Patrick, but Patrick explains that he has broken his net. SpongeBob gives him his old net to use, but he quickly breaks it as well. Finally, SpongeBob gives Patrick his brand-new net and sits there watching as Patrick has fun jellyfishing with it.
Finally, when SpongeBob goes to Squidward's clarinet recital but Squidward tells him that he cannot play in the concert because his clarinet reed is shot. SpongeBob pulls out one of his teeth to replace the reed, and angrily demands Squidward to put on the show, frustrated that the majority of his "Best Day Ever" is ruined. When SpongeBob tries to enter the concert, the doorman will not let him in because he does not have a ticket. He tries various methods of sneaking in but is caught every time. Eventually, the doorman realizes who SpongeBob is, and lets him in because he is on the VIP list. However, the concert ends just as SpongeBob gets into his seat, and that is where he finally loses it.
Reaching his breaking point, SpongeBob goes up on stage, rips the curtains and starts angrily whining to the audience about how his "Best Day Ever" was completely destroyed. However, his friends went up and reminded SpongeBob of how he helped them with their problems out of his kindness, and to make everything up to him, they hold a "very expensive" production in which SpongeBob performs his song, "Best Day Ever," to complete his real Best Day Ever with his friends by his side. After hours, SpongeBob is still singing, his friends are tired and sleepy, the audience has left the concert hall, and the janitor is sweeping the floor. Squidward asks, "How long they will have to keep this up?" and Mr. Krabs replies with "Just until his little heart gives out, Squidward. Just until his little heart gives out."
Squidward's concert outfit is a reference to Sgt. Pepper.
This episode marked the end of the Lowercase/Uppercase Captioning. All captions in this episode are in uppercase, including those in brackets. The first season and the first episode of the second season (including "Something Smells" and "Bossy Boots") used all-Uppercase captioning, except for text in explanation brackets.
SpongeBob's special net was called the Deluxe Jellyfish-Slayer Composite Pro. But in past episodes, it's called the Ol- Reliable. This may be its official name.
In this episode, when SpongeBob is going to Krusty Krab, there is no Chum Bucket across the street.
After the first musical at the beginning of the episodes, nematodes bitten Krusty Krab, instead of flags, there was a skull, few seconds after, the flags are back.
SpongeBob's pants are eaten by the nematodes, but as soon as he gets away from them, they are suddenly back on for the entire rest of the episode.
SpongeBob pulls out his left buck tooth to help Squidward, but when he pushes Squidward into the concert, he has both buck teeth again.
Several seconds elapse between SpongeBob being carried to his seat to when he finally sits down. As soon as he sits, the concert is over and the audience applauds. During that time, the clarinet is not heard, meaning there was a long period of silence on stage until the concert ended.
When Squidward is talking to SpongeBob about how he saved the concert day, Sandy's tail is white instead of brown.
During SpongeBob's musical play, the fake Krusty Krab shows letters that say 'Krusty Krab' on the backdrop, but seconds later, it only says 'KK.'
During the musical number at the end, when SpongeBob sings "It's the best day ever!" the third time, if you look closely, you can see Sandy, Mr. Krabs, Squidward, and Patrick mouthing it even though their voices aren't heard.