The episode begins with a jellyfish swimming by SpongeBob's House, where SpongeBob and Patrick then observe it through a massive telescope protruding from a window at SpongeBob's house. They then slide down ropes (causing them to get rope burn) and put their nets together, and SpongeBob puts on his glasses. They prepare for Jellyfishing like a pro, but then meet Squidward and ask him if he wants to join them. He says that he can't go with them because he is busy and goes bicycling instead. SpongeBob asks Squidward if he can join them next time. Squidward sarcastically says yes and goes off.
Unfortunately, while he is bicycling, he has an accident involving a jellyfish and is ultimately left wheelchair bound. SpongeBob and Patrick decide that what Squidward needs is a "Best Day Ever." It begins at Squidward's house where Patrick offers Squidward some soup. (For whatever reason, the doctors put bandages all over Squidward's body, including his mouth). Patrick blows the hot soup onto Squidward's bandaged face several times before SpongeBob says that soup isn't a good idea. SpongeBob then suggests that some music would be good, and gets Squidward's clarinet. He blows a bad note before realizing that his lips are too dry, and goes through several disgusting motions of trying to wet his lips. Patrick soon violently takes the instrument away from SpongeBob, declaring music not to be a good thing for Squidward either.
SpongeBob and Patrick then declare that a Jellyfishing expedition would be in order for the "Best Day Ever." When they arrive in Jellyfish Fields, SpongeBob tells Patrick to give a net to Squidward, while he finds "a good specimen." He (Patrick) explains that Squidward must, "firmly grasp [the net] it in your hand," but when Patrick fails to put a jellyfishing net in Squidward's cast covered hand, he stabs it through Squidward's palm, much to his chagrin and pain.
He is not into it at first, but when a jellyfish stings him, he goes after it for revenge. He manages to catch the jellyfish, and bangs his net triumphantly against a pink mass, but in doing so, he angers a queen jellyfish, who was the aforementioned pink mass. The queen jellyfish chases after him, attacking him with an extremely massive sting. The next day, SpongeBob and Patrick meet outside Squidward's house, and attempt to give a now life-support-bound Squidward the jellyfish that he caught the previous day. SpongeBob wonders if Squidward is still mad, and Squidward, who is still mad, according to Patrick and based on his actions, opens the jar and lets the jellyfish attack SpongeBob and Patrick, but not before the Jellyfish summons the Queen Jellyfish. As Squidward laughs, the Queen Jellyfish finds him and stings him, destroying his life-support. A completely blackened Squidward can only say, "Ow."
The firmly grasp it quote has become popular on the internet, being a popular meme.
SpongeBob, Patrick, and Squidward are all left handed in this episode.
This is not the first episode to feature a jellyfish, but it is the first to feature the sport of Jellyfishing.
Squidward rode off a cliff, causing an explosion. This was referenced again in the episode "New Fish in Town" and "My Pretty Seahorse," when Squidward stated not to laugh at SpongeBob because of his previous karma, however, he still rode off a cliff.
Patrick says "Merry Christmas!" possibly meaning "Christmas Who?" took place before this episode.
Karma: Squidward releases the jellyfish from its jar to sting SpongeBob and Patrick.
It is possible that SpongeBob and Squidward are actually good friends, because when SpongeBob is waiting for Squidward to return home from the hospital, he looks at a picture of him and Squidward, the caption reading "Friends." SpongeBob has his arm around Squidward and is smiling, and Squidward has his arm around SpongeBob but is frowning, but this could just be because Squidward is never smiling. It is likely that Squidward really cared enough about SpongeBob to pose with him for this photo, thus making them possibly good friends.
In "I'm Your Biggest Fanatic," SpongeBob says that he has never seen a Queen Jellyfish, meaning that this episode takes place after that one.
When Squidward leaves SpongeBob and Patrick on his bicycle, SpongeBob's house is missing.
At the beginning, the sky is blue, but when SpongeBob and Patrick come out of the pineapple, the sky is orange, and when they chase the jellyfish, the sky is blue again.
When SpongeBob says, "Hey, Patrick." Patrick's mouth lip syncing to what SpongeBob was saying.
When SpongeBob and Patrick throw Squidward a Best Day Ever Party, SpongeBob is inside, but when Squidward leaves his house, SpongeBob is shown outside.
When Squidward was in his wheelchair, he needed a cast for each arm, but he was able to move them to slam his jellyfish against the bigger jellyfish.
When SpongeBob and Patrick were chanting "Jellyfishing! Jellyfishing!" at Jellyfish Fields, SpongeBob's mouth doesn't move to the sync.
Squidward's net switches between his hands. First, it is in his right hand, then his left, then right again. This error happens again in "Krabby Road."
When Squidward is on his wheel bed at the end of the episode, when he arrives to the scene he is facing his front door, however later on in the scene he is facing towards Patrick's house when the big jellyfish zaps him.
When SpongeBob says "Hey, Squidward!" his mouth moves as if he were saying something else.
This happens again when he said "There's one in position."