Contestants on Figure it Out getting slimed.
Slime is a (usually) green semi-viscous substance that has been synonymous with Nickelodeon since its introduction on You Can't Do That On Television. It is typically dumped on a person's head in an act of either humiliation or celebration, in an act called being slimed. On You Can't Do That On Television, saying the phrase "I don't know" would result in the speaker getting slimed. Slime has been used on every messy game show on Nickelodeon in some way shape or form, and has become a staple of the Kids' Choice Awards.
Appearances in shows
You Can't Do That On Television
You Can't Do That On Television introduced slime in 1979.
If anyone on the show said "I don't know", they would be slimed. Occasionally, the slime would be a color other than green.
Double Dare
Slime was used in several Physical Challenges and obstacles, including the Slime Canal and the Nick Blimp (which essentially was just the contestant getting slimed).
Wild and Crazy Kids
Slime was only used in one game, but on a few occasions during the "host segments" someone would get slimed. Wild and Crazy Kids would more often use their own slime-like substance, a thicker substance called blap.
Figure It Out
Halfway through the game a "Secret Slime Action" would be announced to everyone but the panelists. Once one of the panelists (usually Danny Tamberelli) performed this action, they would be slimed. Occasionally the slime used on Figure It Out would be yellow. On the revival an extra sliming action, called the "Word of Honor", was introduced, where one of the words in the puzzle would cause the contestant to get slimed.
Weinerville
One cannot have the "Special Topping" in Playland without slime.
Rugrats
In Rugrats in Paris: The Movie, the Ooey-Gooey World ride at EuroReptarland is shown to be filled with green slime.
SpongeBob SquarePants
In the episode "Graveyard Shift", when Squidward is trying to remember the signs that signal the approach of the hash-slinging slasher, he then notices the walls behind him are oozing green slime. He initially thinks this is the third sign, but then remembers, "No, wait, they always do that."
Slime Geyser
One of Nickelodeon's trademarks was the Slime Geyser, a fountain located just outside of Nickelodeon Studios, which would spew the goo upwards every fifteen minutes. In its early days, it would shoot forcefully enough to get those standing too close slimed, though the pressure was reduced in later years. The fountain was removed in May of 2005.
Merchandising
Several slime-related products were created and sold in the past, including Green Slime Shampoo, which was used as a parting gift on Double Dare, and Slime Shoes. A toy called Slime was also made; however, it did not prove to be as popular as the similar Gak.