Jerktonium is a fictional element seen in It's a SpongeBob Christmas!. The antidote for it is the song Don't Be a Jerk (It's Christmas).
Jerktonium is a toxic chemical-filled element is known to make people act mean and change them into jerks (except SpongeBob, due to his pure heart and small brain). They also have big black bushy eyebrows, black baggy eyes and five o'clock shadow.
Plankton discovered the material and planned to use it on people in Bikini Bottom to make himself look good compared to them. His first victim to use it against was SpongeBob SquarePants. He made Spongebob try it but it didn't work on him making Plankton discard the machine. Shortly after that SpongeBob (unknowingly) gives fruitcakes contaminated with Jerktonium to everybody in Bikini Bottom after obtaining the machine from Plankton.
Seeing that the Jerktonium worked on other people in Bikini Bottom except SpongeBob, Plankton constructed his ToyBob to wreck havoc in Bikini Bottom which ruined SpongeBob's reputation.
Later SpongeBob realizes that people in Bikini Bottom were acting like jerks so he decided to ask Sandy Cheeks for help. After getting help, SpongeBob sings the song "Don't be a Jerk" to cure everyone, as they join in. When Santa arrived around the Krusty Krab, he prepares to give everyone (except Plankton) coal and he not only gives Plankton the Secret Formula from Mr. Krabs. Shortly after, ToyBob arrives to wreck havoc, but SpongeBob defeats him with the fruity cake machine in time to save Bikini Bottom causing Plankton's plan to get the Secret Formula to fail due to Santa looking at the remains of the toybob (stating that it's the property of the Chum Bucket). After that Plankton is put back in the Naughty list, and everyone gets a present while Plankton surrenders the formula and gets a bag of coal.