One of Nickelodeon's first staple show was a program from the early 1980's called 'You Can't Do That On Television'. One of its recurring gags was when people got slimed whenever they said "I don't know".
https://en.m.wikipedia.org/wiki/You_Can%27t_Do_That_on_Television
It has remained a trademark of the network ever since.
George doing that Cyberpunk aesthetic before it was cool.