Wanna eat? Shut up then!
This was a phrase popular in Northern Lower Michigan in the mid-to-late 1980's. It is believed to have originated from a highschool teacher in Pentwater trying to calm down a classroom before lunch hour. It was uttered in various circumstances, generally associated with mealtimes.
Kids standing in line at a McDonald's. One turns to the other and shouts (preferably in the other's ear): Wanna eat? Shut up then!