It is laundry day for SpongeBob. He gathers all of his dirty clothes and tosses them into a big pile. SpongeBob loves laundry day and when everything gets cleaned, including the shell on Gary's back. SpongeBob scoops up his pants and dumps them into the washing machine. Afterwards, SpongeBob finishes the day's chores. He washes the dishes, vacuums the floor, and dusts the furniture. Then SpongeBob puts his pants in the dryer, just as Patrick called him on the phone.
On the phone, Patrick asks SpongeBob how long can he make this sound. Before SpongeBob can reply, Patrick begins to yodel loudly into the phone. An hour later, Patrick is still yodeling. SpongeBob tries to interrupt him, but it is no use. Once Patrick started yodeling, there was no stopping him. SpongeBob looks at the clock. His clothes are probably dry by now. He whispers to Gary to check the laundry. Gary inches his way into the laundry room, opens the dryer, and takes out his shell to find out that it is still warm. Gary is so happy to have his shell back that he forgets all about SpongeBob's clothes.
When SpongeBob finally gets off the phone, he hurries to check on the laundry. He is shocked to see that his clothes are still in the dryer. He stops the machine and takes out his pants, only to find out that they had shrunk! He now has to find new pants.
Later that day, SpongeBob goes shopping for pants, but when he walks into his favorite store, Nautical Knickers, he receives some bad news. The store clerk tells SpongeBob that they were out of square pants and the store wouldn't be getting another shipment for months. SpongeBob had to find a different style to meet his needs. He tried on all kinds of pants, but couldn't find anything that he liked. The pants were either too long, too wide, or just plain weird. SpongeBob was about to give up when he found a pair of pants that were almost too good to be true. He tried them on and they were a perfect fit.
A short while later, SpongeBob leaves the store, walking down the street, wearing his new pants. On his way home, he encounters Patrick. SpongeBob asks him if he notices anything different. Patrick says he didn't know who was talking to him. SpongeBob tells Patrick his name to remind of who he was. Patrick looks at a drawing of SpongeBob on his hand. He thinks SpongeBob is still a mysterious stranger because he isn't wearing square pants anymore, so he walks away. SpongeBob couldn't believe it. It's just a new pair of pants and it's not like SpongeBob's friends won't recognize him.
At that moment, Sandy walks by. Sandy says she didn't recognize this stranger in those newfangled dungarees. SpongeBob is shocked that Sandy didn't recognize him either! The pants really made him look like a different person. SpongeBob keeps walking. He is almost home when he spots Squidward. SpongeBob thinks Squidward would recognize him and says "Hi" to him, but Squidward was pretending not to recognize SpongeBob so he wouldn't have to talk to him. SpongeBob believes that Squidward really didn't know who he was. SpongeBob walks away feeling a little sad. SpongeBob is upset that no one recognized him anymore and thinks that starting all over again would be the best solution. He wandered around for a while, not sure what to do. Hours later he spots the Krusty Krab, which cheers him up immediately. SpongeBob happily heads towards the restaurant.
When SpongeBob arrives at the Krusty Krab, he marches straight to the cashier's counter. SpongeBob tells Squidward at the cash register that his name is "SpongeBob RoundPants" and he would like to apply for a position at the fine eating establishment. Squidward nearly falls over. His plan to pretend not to know SpongeBob didn't work. SpongeBob was back to pester him! Squidward had no choice but to play along. He hands SpongeBob a job application. As SpongeBob fills it out, Mr. Krabs walks in and asks what is going on. SpongeBob says he's filling out an application, but Mr. Krabs orders him to work immediately.
SpongeBob can't wait to start his "new" job. He puts on his Krusty Krab employee hat and turns to Squidward. He leads SpongeBob around the restaurant, showing him what to do. In no time SpongeBob learns how Squidward does his job and picks up all of his bad habits. Later on, SpongeBob does his job just the way Squidward has shown him. He was rude to the customers, he turned Krabby Patties, and he kept going to the bathroom. Squidward was proud of him.
When Mr. Krabs walks into the restaurant, he is shocked to see a long line of angry customers along with both SpongeBob and Squidward asleep at the register. Mr. Krabs tells SpongeBob that he's used to Squidward sleeping on the job, but he expects more from Mr. SquarePants. SpongeBob explains to Mr. Krabs that he's not a SquarePants with RoundPants. Mr. Krabs suggests that SpongeBob should take off the pants.
Moments later, SpongeBob comes out of the kitchen in his underpants and is happy to be SpongeBob SquarePants again, serving regular delicious Krabby Patties with a smile. Just then Sandy walked into the Krusty Krab and notices SpongeBob right away. Sandy saw what SpongeBob had on and called him "SpongeBob UnderPants." SpongeBob screams. It had been bad enough being SpongeBob RoundPants. Now he'd have to start all over again as SpongeBob UnderPants!