The Rule Of Nick
A widely accepted social courtesy asking that a given situation, object and/or set of circumstances should be left in the state it was found in; i.e. cleaning up after oneself out of respect for those that may follow after you.
A: "Ugh, Alex made her powdered peanut butter with the Brita water and broke The Rule Of Nick again."
B: "She forgot to switch it back? What else is new..."
B: "She forgot to switch it back? What else is new..."