Squidward is working at the Krusty Krab, and SpongeBob accidentally karate chops him. Squidward asks what he was doing and SpongeBob tells him that he is planning to do karate with Sandy, which Squidward thinks is stupid. That night, Squidward is grocery shopping, and is approached by a large thug (The Creepy Creeper). Squidward assumes he is going to steal his groceries, so he runs to SpongeBob, and asks to be taught karate. SpongeBob then tries to teach him but because he's not very good at it himself, he is unable to teach Squidward.
They then go to Sandy for help. First, she makes Squidward promise not to use it for revenge and use it only for protection. Then, she and SpongeBob try to teach him, but can't. Sandy then decides to quit on him, but Squidward says he'd do anything. So Sandy makes him do all the work around the treedome saying that it will teach him the basic movements. Finally, Squidward decides to quit, however he accidentally flings acorns at himself that he was able to dodge. He then found out that in doing all the work, he actually did learn it.
So then, Sandy presents him his belt to show that he knows karate, but Squidward claims that he has "important business" to attend. He then finds the thug, and uses karate to beat him up (with a lot of the moves being related to the housework he did around the treedome).
However, it turns out that he never wanted to steal his groceries, he wanted to return them. SpongeBob and Sandy then came giving Squidward his belt only to find out that he used karate for vengeance. Sandy says that Squidward doesn't deserve his belt and she and SpongeBob walk away because Squidward dishonored their trust in him. Squidward is then arrested for assaulting the thug.
Irony: Squidward could've just called the police about the so-called "criminal" instead of going through all the trouble of learning karate, and getting arrested for assaulting someone with it.
Strangely, when SpongeBob, Sandy, and Patrick all learned karate, they all wore Karate Gear; however, Squidward never did.
This is the second time SpongeBob's half bodies can talk to each other. The first was "I Had an Accident."
Running Gags: SpongeBob getting sliced in half and characters criticizing Squidward's body by saying "What with the rubbery arms and the doughiness in the middle,". Also, SpongeBob saying, "You missed a spot." when Squidward did Sandy's chores.
This episode's title is a spoof of "Self Defense."
The way how Squidward had to do chores is similar to the film, The Karate Kid, to which the main character, Daniel was tricked by Mr. Miyagi to do chores at his house.
When SpongeBob says "Creepy Creepers lurking behind every corner," this might have been a reference to the Creepers in the popular sandbox game, Minecraft. When SpongeBob states that they are lurking behind every corner, this is also a reference to Creepers in Minecraft since Creepers have been known to commonly ambush the player by walking up to them from around a corner.
When SpongeBob and Sandy first met in "Tea at the Treedome," it was revealed that both of them knew karate before they met each other. In this episode, SpongeBob tells Squidward that Sandy taught him karate, which obviously couldn't have happened before they met. Also, SpongeBob is not very skilled in this episode, when he is in episodes such as "Karate Choppers."
When Squidward first bangs on SpongeBob's door and the scene changes over to SpongeBob and Gary, they were sitting on the couch. After SpongeBob lets Squidward into his house and was spooked by Gary, the couch was missing and Gary was suddenly on the floor.
When Squidward watered Sandy's lawn, Sandy was missing her tail.
Sandy was darker than usual in the night scene.
Sandy's teeth turned dark white when Squidward says "Oh...whatever. Hiyah..."
The toilets are in the wrong place they appear on the left side of the restroom area instead of on the back.