April Fool's Day
April Fool's Day tradition starts in France in 1582 with the adoption of Gregorian calendar which moved the New Year's Day from April 1 to January 1.
Many people either refused to accept the new calendar or were not aware of the changes taking place and continued to celebrate New Year on April 1st. The rest took to calling these people "fools", ridiculing them and playing pranks on them. Over time this developed into tradition in many countries and today the day is celebrated by carrying out practical jokes and hoaxes.