F.U.N. – 1x21
Original air date: September 18, 1999
SpongeBob tries to be friends with Plankton, whom SpongeBob thinks is only evil because he's lonely and made fun of. But Mr. Krabs doesn't believe it. He knows Plankton is evil on the inside. He puts Plankton to the test only to prove to SpongeBob that Plankton is only after the formula.