Flats the Flounder

Flats  the Flounder, also spelled as Flatts the Flounder, is a character who first appears in the episode "Sandy's Rocket."

Description
He is a light olive-green flounder who has light yellow eyes. He wears a light orange, dark green shirt, and light reddish-brown pants.

"Sandy's Rocket"
Flats first appears as a cameo in this episode, where he is one of SpongeBob and Patrick's "alien hunting" victims. He opens a mirror, revealing SpongeBob inside who captures him.

"Texas"
Flats attends 's Texas party where he is holding a square. He is amongst the people who gather around Sandy and cheers when Sandy decides to stay. When Patrick brings up "dumb ol' Texas", Flats and everyone else frowns, most likely worried that Sandy will get furious again.

"The Bully"
He joins Mrs. Puff's Boating School and wants to kick SpongeBob's butt. SpongeBob, afraid and concerned for his safety, makes many attempts to reason with and/or escape him, but to no avail. He eventually calls to protect him, only to find out that Flats is friends with him and that they were community college friends.

He also tries to go to Mrs. Puff to help, who talks to Flats and explains to SpongeBob that "kicking his butt" means that Flats wants to become his friend, which is obviously not true. He then encounters Flats' dad and confronts him about his son's actions, only for the latter to go up to his father and teach him a lesson about talking to strangers, threatening to harm one of his parents.

Flats goes as far as to chase SpongeBob out of school into town, even trying to run him over with a garbage truck. However, said garbage truck slips on a banana peel and flips over, critically injuring Flats in the process. He wakes up in the hospital and learns that SpongeBob saved his life through CPR, yet he is still eager to kick SpongeBob's butt.

Eventually, Flats corners SpongeBob in his own house and proceeds to "kick his butt" by repeatedly hitting him. However, SpongeBob discovers that his soft spongy body simply absorbs the blows and the punches do not harm him in any way. Relieved, SpongeBob allows Flats to attack him throughout his routine.

Flats continues to hit SpongeBob throughout the whole week until he finally passes out from exhaustion one morning at Boating School. While SpongeBob makes his speech that Flats is the true victim, he raises his fist. Mrs. Puff suddenly arrives and, upon seeing SpongeBob's raised fist and Flats unconscious, believes that SpongeBob beat up Flats and thereby threatens to harm SpongeBob in the same way Flats was harmed at the end.

"The Slumber Party"
He is seen at 's party, colored as Incidental 68. Two copies of Flats are visible in the crowd, marking the only time his model is used twice in the same scene.

"Squid Noir"
He is one of the customers seen in the Krusty Krab, covering his ears due to Squidward's poor clarinet playing.

"Don't Feed the Clowns"
He is a customer of the bakery who gets knocked out by getting hit with a pie thrown by Incidental C1.

"SpongeBob's Big Birthday Blowout"
Flats makes a cameo at SpongeBob's birthday party.

The SpongeBob SquarePants Movie video game
A drawing of him can be seen in Squidward's house in the PC version.

Role in The SpongeBob Movie: Sponge Out of Water
He is seen in the end credits with other Bikini Bottomites.

Trivia

 * He has only made one major appearance in the series to date, with that being in the episode “The Bully”.