Flats the Flounder is a green flounder who first appeared in the episode Sandy's Rocket. He was the bully of Mrs. Puff's Boating School. He was born in 1980. He made his only major appearance in the episode The Bully. He is a violent, sociopathic flat flounder who likes to kick people's butts and pathologically control others through violence, charm and persuasion. When he breaks into SpongeBob's house and finally kicks SpongeBob's butt, it doesn't hurt because SpongeBob is made from "Some kind of spongy material". This tired Flats drops dead on the floor. He also has a father who he tells not to talk to strangers. He also appears in other episodes in cameos, such as Sandy's Rocket. Flats obviously first appeared in the episode Sandy's Rocket, but his name was unknown during that time. He went to community college with Patrick. In the episode, he gets sent to The Hospital as a result of chasing SpongeBob. He is voiced by Tom Wilson.
 Known Relatives
 Known Friend(s)
Flats had green scales, he had a very big body, he wore an orange colored shirt with a green stripe and a green collar, and some brown pants. His eyes are aligned near-vertically at the top of his face.
 Friends and enemies
Flats is most likely enemies to SpongeBob, possibly because he said "Hi! I'm SpongeBob!", but to his surprise, Patrick mentions over the phone that he actually went to college with Flats, whilst SpongeBob overreacted by screaming. This is also supported by the fact that Flats repeatedly threatens to kick Spongebob's butt.
- "No, I mean it."
- "Dad, what are you doing? What did I tell you about talking to strangers?"
- "Yeah, except you forgot about the part where I kick your butt!"
- "Wow, I’m touched. I’ll have to remember that when I’m kicking your butt."
- "It's butt-kicking time!"
- "Those flowers for me?"
- "I'm gonna kick your butt twice as hard."
- "Hi Spongebob, I'm gonna kick your butt!"
- Flats also appeared in Sandy's Rocket and Texas as a minor character. Flats was known as an "alien" to SpongeBob and Patrick.
- Flats's voice actor, Tom Wilson, also played all of the antagonists in the Back to the Future trilogy, the bully Biff Tannen and his family members that the protagonist, Marty McFly (Michael J. Fox) meets through different parts of time he travels to.