Mermaid Man and Barnacle Boy are watching TV in Shady Shoals, when SpongeBob and Patrick suddenly appear and wake then up. Mermaid Man attacks SpongeBob with the "Mermerang", thinking he is a supervillain, and in the resulting incident Mermaid Man and Barnacle Boy are injured and sent to the hospital.
While SpongeBob and Patrick go to the hospital to visit them, Mermaid Man and Barnacle Boy receive a call from the police commissioner, telling them that they will be celebrity guest contestants at the Bikini Bottom shuffleboarding competition. They are unable to attend in their condition, but SpongeBob then says both he and Patrick are both certified Mermaid Man and Barnacle Boy impersonators. They are given rings which produce rubber Mermaid Man and Barnacle Boy costumes, and are told to immediately return then after the tournament.
After they win the shuffleboarding contest, they go to return the costumes, but Patrick convinces SpongeBob that if they don't save the town from evil, no one will. They begin throwing everyone they see in jail for completely unjustified reasons (including throwing away a Krabby Patty, chewing gum too loudly, and being "too old"). Eventually, they have arrested nearly everyone in Bikini Bottom, and decide to return the costumes. However, they see Man Ray entering a laundromat, and despite the fact that he is doing absolutely nothing wrong, follow him in and arrest him after a fight scene, involving throwing Man Ray's head in the dryer, causing it to shrink. The jail is now so full of people that it literally explodes, causing people to fall down from the sky.
SpongeBob and Patrick return the costumes, and Mermaid Man and Barnacle Boy leave the hospital, but are confronted by an angry mob of the people SpongeBob and Patrick wrongfully arrested, who start chasing them and SpongeBob and Patrick confuse them for fans.
This is considered one of the worst episodes because there is no shuffleboarding in the episode, even though they mentioned it a bunch of times, and SpongeBob and Patrick cruelly arresting people for silly reasons.