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. Flats' body is shown to be somewhat two-dimensional, hence his name.
Flats is twice injured in his appearance. First, he runs over a banana peel in the middle of the street while driving, which subsequently hospitalizes him. He seemed to have undergone a fatal accident, as his entire body is covered with bandages. However, later in the episode, he is shown to have recovered, as he is no longer bandaged during his final confrontation with SpongeBob. During said confrontation, Flats' health starts to deteriorate as he loses energy from persistently punching SpongeBob, eventually knocking him unconscious at school.
Being a bully, Flats is very sadistic, merciless, rude, intimidating, and unrepentant for no apparent reason. This is established when he reveals kicking other people's butts as his main interest. This is also evident when he still wants to hurt SpongeBob even after the latter saved his life from a vehicular accident, showing no remorse to the situation whatsoever. He is also shown to be disrespectful to authority figures, as he confronts his dad about talking to strangers and threatens to kick his butt. This intimidates his dad, who is too scared to punish his son for his actions.
Despite his rudeness, authority figures view his threatening behavior as friendly and well-intentioned, when it obviously is anything but.
However, he is shown to have made up with SpongeBob in "SpongeBob's Big Birthday Blowout" as he no longer exhibits any antagonism towards him and even helps throw his surprise party.
Abilities and talents
Driving: Flats is shown to be proficient at operating motor vehicles, as seen when he drives a garbage truck down the street. However, he fails to defend himself against an unsuspected banana peel on the road.
Fighting: While he is unsuccessful in attacking SpongeBob due to the latter's status as an invertebrate, he is implied to have inflicted serious physical harm to his previous victims.
Strength: He was strong enough to rip his own chest hair off without feeling any pain, and later knock SpongeBob's door down.
Role in series
Flats first appears as a cameo in this episode, where he is one of SpongeBob's "alien hunting" victims.
He joins Mrs. Puff's Boating School and wants to kick SpongeBob's butt. SpongeBob, concerned for his safety, makes many attempts to reason with and/or escape him, but to no avail. He eventually calls Patrick 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 intent on kicking his 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. The aftermath is that SpongeBob is seen with his fist raised in the air, requesting Mrs. Puff's attention; however, the latter misinterprets the situation by deeming that SpongeBob knocked Flats unconscious, and thereby threatens to harm SpongeBob in the same way Flats did at the end.
He is a customer of the bakery who gets knocked out by getting hit with a pie thrown by little clown.
"SpongeBob's Big Birthday Blowout"
Flats makes a cameo at SpongeBob's birthday party.
Flats is a flounder, which is a species of flatfish, who have both eyes on one half of their body.
It is never really explained why he wants to kick SpongeBob's butt, though it is speculated to be for revenge for SpongeBob trapping him in "Sandy's Rocket." Bikini Bottom Mysteries Season 1 Episode 10 further investigates the mentioned speculation through Exhibit A.