April Fool's Day, also known as Wan Fool's Day and Humor Day, falls on April 1. April Fool's Day jokes can only be played before 12 noon, which is a strict and established rule. The man who was having fun after noon was a bigger fool than the man he made fun of. Anyone who jokes after the hour will hit a snag immediately and find it boring. There is a little poem that describes it like this: April Fool's Day is past twelve o'clock, you big fool came late. By April Fool's Day next year, you'll be the biggest idiot.