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's where he finally loses it. Hysterically frustrated, SpongeBob goes up on stage and starts angrily whining to the audience about how his "Best Day Ever" was completely destroyed. However, his friends then remind 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, "The 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."
( ‣ ) Associated production music
( • ) Original music
( ◦ ) SpongeBob music
• ? - Sage Guyton, Jeremy Wakefield [title card] ◦The Best Day Ever - Andy Paley, Tom Kenny [opening] ‣The Jitters - Raymond C. Jones [Krusty Krab condemned] ‣Drama Link (h) - Hubert Clifford [Krabs faints] ‣Drama Link (d) - Hubert Clifford ["I'm gonna have to ask you to leave."] ‣Tympup A and Hawaiian Sting - Nicolas Carr [nematodes eat SpongeBob's pants] •Vibe Sting - Nicolas Carr ["Huh?"] •Pied Piper Bob - Nicolas Carr, Barry Anthony [SpongeBob leading nematodes away] ‣ ? [nematodes fall asleep] •Goofy Conversation - Nicolas Carr, Barry Anthony [adhesive karate gloves] ‣Take That! (b) - Helene C.E. Muddiman [SpongeBob jumps out at Sandy] ‣ ? ["Oh, just a little something I like to call karate!"] •Goofy Conversation - Nicolas Carr, Barry Anthony [leak in Sandy's roof] ‣Take That! (b) - Helene C.E. Muddiman ["Knock... it... off!"] • ? - Nicolas Carr ["It stopped?"] •Steel Link (c) - Jeremy Wakefield [karate glove stuck to Sandy's roof] •Gator - Steve Belfer [Patrick jellyfishing] ‣Fates - Gregor F. Narholz ["I broke my net!"] •Gator - Steve Belfer [SpongeBob gives Patrick his old net] ‣Fates - Gregor F. Narholz [Patrick breaks it] • ? - Jeremy Wakefield ["Actually, Patrick, that's my brand new net."] •Gator - Steve Belfer [Patrick jellyfishing with SpongeBob's new net] ◦The Best Day Ever - Andy Paley [SpongeBob's sad; steel guitar version] ‣Facing the Challenge - Gregor F. Narholz ["I won't let this one slip through my fingers."] ‣Woe is Me! - Richard Myhill [Squidward's clarinet reed is broken] ‣Big Ed's March - Sam Spence [SpongeBob replaces it with one of his teeth] ‣Tomfoolery - David Snell [SpongeBob doesn't have a ticket] ‣ ? [marionettes] ‣ ? [SpongeBob sneaks into the theater] ‣ ? [Mrs. Puff arrives] • ? - Nicolas Carr ["Wait a minute."] ◦The Best Day Ever - Andy Paley [reserved seat; marching band version] • ? - Nicolas Carr ["Huh?"] ‣Romantic Ending - Harry Bluestone, Emil Cadkin ["This was supposed to be my perfect day."] ‣Hawaiian Cocktail - Richard Myhill ["No, it's not okay!"] ◦The Best Day Ever - Andy Paley, Tom Kenny [ending]
On The Complete 4th Season Volume 2 DVD, there are bonus shorts (A Random Act of SpongeBob shorts) and a karaoke music video using episodes of SpongeBob.
Ed, Edd, n Eddy, one of Cartoon Network's most popular shows, had a marathon of a similar name called the "Best Day Ed-Der".
Squidward's band uniform 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.
In "Jellyfishing", SpongeBob and Patrick arrange a "Best Day Ever" for Squidward.
The "Best Day Ever" song was first featured as the seventh track on the soundtrack and the last song in the credits before it ends in The SpongeBob SquarePants Movie, a while before this episode was made.
For some reason, along with The Gift of Gum, this episode didn't air in the Netherlands until May 9, 2010. Although, the rest of season four had already aired back in 2006.
While SpongeBob was playing his nose, and starts getting tired, the tone of the sound is the same as the Best Day Ever song.
This special celebrates the unoffical 30th anniversary of Nickelodeon.
In this episode, when SpongeBob is going to Krusty Krab, there is no Chum Bucket. A similar mistake happened in Suds.
Spongebob's pants were 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.
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.
SpongeBob pulls out his left buck tooth to help Squidward, but when he pushes Squidward into the concert, he has both buck teeth again.
When Squidward was talking to SpongeBob about how he saved the concert day, Sandy's tail is white instead of brown.
In SpongeBob's vision, Sandy was wearing her protective suit, and SpongeBob was not wearing a helmet. Since this was just a vision, that was just SpongeBob's imagination.
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 it's official name.
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, we never heard the clarinet, meaning there was a long period of silence on stage until the concert ended.
During SpongeBob's musical play, the fake Krusty Krab shows letters that say 'Krusty Krab' on the backdrop, but two seconds later, it only says 'KK'.
For some reason, Mrs. Puff is only just arriving as the concert is ending.
It is weird how SpongeBob is on the V.I.P. list for Squidward's clarinet recital, because Squidward hates SpongeBob. It's possible he added him after SpongeBob helped him save his recital.
Strangely when Squidward's concert was over he recived thunderous applause, this apparently means that Squidward actually has played the clarinet in success and everyone's liking despite his failures in recent episodes, however, in episodes opened up after this one his clarinet abilty is strangly gone as he returns to his mediocre way. Maybe using SpongeBob's tooth for a reed made him do better.
SpongeBob's pants were ripped of by the nematodes and his sleeves off but when there were swirling SpongeBob's pants there weren't even ripping on them.
Even though this episode is a regular 11 minute episode, it was believed by some fans to be double-length.