Fruitcake

It's a SpongeBob Christmas!
The Fruitcake was the medium used by Plankton to transfer the Jerktonium into the Bikinibottomites. The Carolers were the first people to eat the fruitcake, SpongeBob was the second. No matter how much Jerktonium laced fruitcake SpongeBob was given, he still was not affected. This was due to his pure heart. Some rumor that due to where it was created the fruitcake might be made from chum minus the letter h. (hence the name of the resturant)

Christmas Who?
The Fruitcake played a very minor role in Christmas Who?. Mr. Krabs presented it to Plankton during the main song.