SpongeBob SquarePants - Season 1 Episode 21 F.U.N. Be there and be square!
Overview: SpongeBob thinks that Plankton is evil only because he is lonely and has no friends. SpongeBob becomes Plankton's friend and plays with him. But, Mr. Krabs is convinced that Plankton is evil and that SpongeBob should not be hanging around with him.