Some scenarios that may or may not have occurred on the first of April through history.
1698: A group of people is sent to the Tower of London to "see the lions washed."
1708: Well-known astrologer John Partridge, whose death had been foretold to take place on March 29 by previously unknown rival astrologer Isaac Bickerstaff, and whose death was then reported as having taken place March 30 by that same Bickerstaff, walks the streets of London and finds everyone who knows him treating him as if he were a ghost. In fact, so many people are so sure that he is dead that his astrology career is no longer viable. Which was the intention of the man posing as Bickerstaff, a critic of astrology named Jonathan Swift.
1789: I swear I am not making this up: The House of Representatives formed its very first quorum and conducted its very first business on April 1, 1789.
1957: The respected BBC news how Panorama announces that thanks to a mild winter and the virtual elimination fo the dreaded spaghetti weevil, Swiss farmers are enjoying a bumper spaghetti crop. Footage shows Swiss peasants pulling spaghetti from trees.
1966: Flann O'Brien, Irish humorist, drinks himself to death with exquisite timing at age 54.
1967: The United States Department of Transportation begins operation. Once again…not making this up.
1974: The residents of Sitka, Alaska awake to see smoke arising from the supposedly dormant Mt. Edgecumb. Panic begins to take hold until someone figures out that local wise guy Porky Bickar has flown a huge pile of old tires into the crater and set them on fire.
(Source: Wikipedia, Museum of Hoaxes)