A term was originally used in the Park Hill South High School cafeteria meaning that the students are to be clean while eating and throw away all of their trash when they are finished so it makes the janitors' jobs easier. It is commonly yelled out with a response shout of "Tidy Friday" by the audience.
Ms. Sharon- "Tidy Friday"
Students- "Tidy Friday"
Remember, today is Tidy Friday. Pick up your mess.