An entirely unwritten and yet widely accepted variation to the Eleven Minute Rule. The Dr. Rule states that if you are sitting in class for fifteen minutes (rather than the eleven provided a professor without a doctorate) and no professor has shown up, you are allowed to leave class without penalty.
Guy 1: "Dude, it's been 11 minutes we can totally leave class now!"
Guy 2: "No man she's a Doctor, we have to wait four more minutes."
Guy 1: "Oh right....the Dr. Rule....where is that actually written?"