As per the common belief, during the reformation of the calendar the date for the New Year was moved from April 1st to January 1st. Some chose to simply ignore the change and some merely forgot. These people were considered "fools" and were subjected to some ridicule, and were often sent on "fools errands" or were made the butt of other practical jokes. This harassment evolved, over time, into a tradition of prank-playing on the first day of April. The tradition eventually spread to England and Scotland in the eighteenth century. It was later introduced to the American colonies of both the English and French. April Fool's Day thus developed into an international fun fest, so to speak, with different nationalities specializing in their own brand of humor at the expense of their friends and families.
In modern day France, the first day of April is called "Poisson d'Avril" or "April Fish." An April fish is a young fish and thus, one which is easily caught. French children fool friends by taping a paper fish to the victim's back and, when the "fool" discovers this trick, yelling: "Poisson d'Avril!" Traditionally, French pranks must include a fish (or at least a vague reference to same within the joke) and it is not unusual for friends to be presented with dainty presents fashioned in the form of a small fish on All Fool's Day. The nickname of "Poisson d'Avril" is said to have been "acquired" by Napoleon I (Bonaparte) when he married Marie-Louise of Austria on Apri 1, 1810.
In Scotland, where the tradition is celebrated over the course of forty-eight hours, April Fool's Day is also known as "April Gowk," "Gowkie Day" or "Hunt the Gowk." "Gowk" is Scottish for "cuckoo" (an emblem of simpletons) and thus, a "gowk" is the butt of any practical joke. The second day of the Scottish April Fool's custom is devoted exclusively to pranks involving the posterior region of the body. This is known as "Taily Day" and the origin of the ever-popular "Kick Me" sign is likely traceable to this observance. The same custom takes place in the Orkney Isles (located just off the Scottish Mainland), where this area's "Tailing Day" is also celebrated on April 2.
In England, where tricks and pranks are only permissable during the morning hours of All Fool's Day, the victim is known as a "noodle." In the Cornwall region of England, an April Fool is also known as a "gowk" (as in Scotland) or a "guckaw." If a child is successful in playing a trick on another, then it is usual for the perpetrator to taunt: "Fool, fool, the guckaw!." On the other hand, if the victim fails to fall for the trick, then the retort is: "The gowk and the titlene sit on a tree...you're a gowk as well as me!" A "titlene" is a hedge sparrow. In the County of Cheshire in England, an April Fool is an "April Gawby," sometimes referred to as a "gobby" or "gob," while in Devon, unlike the remainder of England, pranks are allowed in the afternoon and the custom of pinning an inscription such as "Please kick me" to the coat-tails of an unsuspecting victim is popular (again, much as it is in Scotland). In Devon, however, this is known as "Tail-Pipe Day." In the Lake District area of England, an April Fool is an "April Noddy" and at the end of the day, it is customary to chant: "April Noddy's past and gone...You're the fool an' I'm none".
In Mexico, April Fool's Day is observed on December 28. Originally a sad remembrance of the slaughter of the Innocents by King Herod, it eventually evolved into a much lighter commemoration involving pranks and trickery.
In Portugal, April Fool's Day is celebrated on the Sunday and Monday prior to the Lenten Season, with the traditional trick being to throw flour at one's friends.