One morning in Bikini Bottom, SpongeBob tells Squidward it's time for work, and says "another day another dollar" but Squidward says more like another nickel, which makes SpongeBob laugh uncontrollably. Squidward then goes through a whole day at work with SpongeBob laughing, and even at night. The next day at work, after SpongeBob told the "nickel joke" to the customers, Squidward has decited he has had enough of SpongeBob's incessant laughter. He then sees SpongeBob hurting himself when he laughs, so he tricks him into believing that SpongeBob has a laugh-related illness. According to the made-up disease, if SpongeBob laughs one more time in the next 24 hours, his laugh box will explode and he will never laugh or giggle again. For the rest of the day, SpongeBob fights every single urge to chuckle. First, he sees Patrick trip over a banana peel several times, and runs away. Next, he sees that whoopee cushions are all over the town. Last, he sees a pie truck in an accident and some of the pie land on some fish. In a drastic measure, he buries himself to never be interrupted by a joke during the night. The next morning, SpongeBob discovers that he has completely lost the ability to laugh. He tells Patrick that he has lost his laugh, but when Patrick looks inside SpongeBob and lights a match, he runs around in circles. Later, SpongeBob goes to the Krusty Krab to tell Mr. Krabs that he has lost his laugh. Mr. Krabs says that money always makes him laugh, but SpongeBob doesn't feel a tickle. Next, SpongeBob consults Sandy. Sandy gives SpongeBob books about laughter. SpongeBob reads the books, but still doesn't have any effect on his laugh box. Now utterly grief stricken, all SpongeBob can do is cry his eyes out, meaning more noise than ever. Feeling guilty but still wanting peace and quiet, Squidward finally confesses to the sad SpongeBob, as the weeping has been more annoying than SpongeBob's giggles and after Squidward admits everything, SpongeBob laughs to see it has been a good joke and Squidward joins in the laughter. When Squidward says "You even fell for the thermometer in the boiling oil routine!" SpongeBob immediately stops laughing, and goes inside his house. When Squidward laughs too much, he is taken to the hospital. Later, it is revealed that Squidward has lost his laugh and Dr. Forrest points out that someone has given him half of their laugh box. It isn't Patrick, Sandy or Mr. Krabs; it was SpongeBob. Squidward starts to laugh like SpongeBob and runs out of the building. SpongeBob then says "Ah, there he goes off to share his laugh with the world", followed by his laughter.
This is generally considered to be one of the most annoying SpongeBob episodes, mainly because of SpongeBob's constant laughter.
Later that same evening
This episode was originally going to be called "Unfunny Pants", but when it aired on Nick, it was changed to "Laughbox", and then was later changed to "Funny Pants".
The title card is similar to Squirrel Jokes, which gets these two episodes confused.
Squidward never laughs like SpongeBob again. This could mean that this happened at the end of the SpongeBob timeline, or that Squidward got some kind of surgery to reverse the operation back to his own laugh.
SpongeBob first used the line "Another day, another dollar" in the episode Krabby Land.
The plot of this episode is very similar to the episode Fools in April. In both episodes, Squidward plays a prank on SpongeBob in order to get some peace and quiet, SpongeBob becomes greatly saddened and depressed because of Squidward's prank, and towards the end, Squidward apologizes and then runs off laughing maniacally.
The fez hat Squidward is wearing when he says SpongeBob became a sad sack is also seen in Good Neighbors.
The laughing machine SpongeBob is attached to is similar in appearance to an "iron lung" breathing aid.