Squidward, the Unfriendly Ghost": When SpongeBob and Patrick believe they have killed Squidward and that he is now a ghost, he takes advantage of this by making them his slaves. Eventually, SpongeBob and Patrick, after reading a magazine about the Flying Dutchman's death, get the idea that Squidward is being mean and angry because he was never put to rest. SpongeBob and Patrick attempt to bury Squidward, which ultimately brings him to confess that he is actually alive. However, SpongeBob and Patrick still think that Squidward is a ghost in denial and send him to the "great beyond" by trapping him in a bubble, which floats up into the sky where the pelicans are.
Fools in April": Squidward gets annoyed with SpongeBob pulling playful and harmless pranks on people at the Krusty Krab, and pulls a very cruel and harmful prank on SpongeBob in retaliation. Squidward then laughs at him when he comes out of the trash, which makes SpongeBob run out of the restaurant sobbing hysterically, and the Bikini Bottomites turn on him. Squidward tries to apologize, but he is physically unable to apologize until the very end of the episode, where SpongeBob has the last laugh: all of his friends were standing behind him in his house and witnessed Squidward's apology. As a result, Squidward suffers a mental breakdown and runs off back to his house laughing maniacally after shouting that he had just fooled them as well.
"Grandma's Kisses": Squidward and the customers at the Krusty Krab ruthlessly tease SpongeBob for having a kiss on his forehead given by his grandma. At the end of the episode, it is shown that they have been spying on SpongeBob with his grandma through her house's window.
That Sinking Feeling": He tried to separate SpongeBob and Patrick by drawing a line, and later, he threatened them that if Squidward's house was not back to normal on the count of three, he will grind them into chum (kill them).
Little Yellow Book": Squidward reads SpongeBob's work diary in front of the customers, which made SpongeBob sad. He sees that he has been known as a "diary thief," but does not feel be until his house was repossessed. Later, he even reads SpongeBob's personal diary, and doesn't even show regret of his actions even after he begs for SpongeBob to forgive him.
Tried to kill SpongeBob and Patrick several times
Read SpongeBob’s Diary,which is invasion of Privacy and theft
He also enslaved them few times
He will kill them if they annoying him too much which is petty