April Fools!

Origins
 
A ticket to "Washing the Lions" in London from 1857. This traditional April Fools prank is first recorded in 1698.In Chaucer's Canterbury Tales (1392), the "Nun's Priest's Tale" is set Syn March bigan thritty dayes and two. Chaucer probably meant 32 days after March, i.e. May 2, the anniversary of the engagement of King Richard II of England to Anne of Bohemia, which took place in 1381. However, readers apparently misunderstood this line to mean "March 32," i.e April 1. In Chaucer's tale, the vain cock Chauntecler is tricked by a fox.

In 1508, a French poet referred to a poisson d’avril (April fool, literally "April fish"), a possible reference to the holiday. In 1539, Flemish poet Eduard de Dene wrote of a nobleman who sent his servants on foolish errands on April 1. In 1686, John Aubrey referred to the holiday as "Fooles holy day", the first British reference. On April 1, 1698, several people were tricked into going to the Tower of London to "see the Lions washed. The name "April Fools" echoes that of the Feast of Fools, a Medieval holiday held on December 28.

In the Middle Ages, New Year's Day was celebrated on March 25 in most European towns. In some areas of France, New Year's was a week-long holiday ending on April 1 So it is possible that April Fools originated because those who celebrated on January 1 made fun of those who celebrated on other dates. The use of January 1 as New Year's Day was common in France by the mid-sixteenth century, and this date was adopted officially in 1564 by the Edict of Roussillon.

In the eighteenth century the festival was often posited as going back to the time of Noah. According to an English newspaper article published in 1789, the day had its origin when Noah sent his dove off too early, before the waters had receded; he did this on the first day of the Hebrew month that corresponds with April.

Well-known pranks

Lists of miscellaneous information should be avoided. Please relocate any relevant information into appropriate sections or articles.

Alabama Changes the Value of Pi: The April 1998 newsletter of New Mexicans for Science and Reason contained an article written by physicist Mark Boslough claiming that the Alabama Legislature had voted to change the value of the mathematical constant pi. This claim originally appeared as a new A story in the 1961 science fiction novel Stranger in a Strange Land by Robert A. Heinlein, however see also the actual Indiana Pi Bill.

Spaghetti trees: The BBC television programme Panorama ran a famous hoax in 1957, showing Italians harvesting spaghetti from trees. They had claimed that the despised pest, the spaghetti weevil, had been eradicated. A large number of people contacted the BBC wanting to know how to cultivate their own spaghetti trees. It was, in fact, filmed in St Albans.

Left Handed Whoppers: In 1998, Burger King ran an ad in USA Today, saying that people could get a Whopper for left-handed people whose condiments were designed to drip out of the right side. Not only did customers order the new burgers, but some specifically requested the "old", right-handed burger.

Taco Liberty Bell: In 1996, Taco Bell took out a full-page advertisement in The New York Times announcing that they had purchased the Liberty Bell to "reduce the country's debt" and renamed it the "Taco Liberty Bell." When asked about the sale, White House press secretary Mike McCurry replied tongue-in-cheek that the Lincoln Memorial had also been sold and would henceforth be known as the Lincoln Mercury Memorial.
 
Wikipedia's Main Page on April 1, 2007. The featured article write-up purposely confuses U.S. President George Washington with an inventor of the same name.San Serriffe: The Guardian printed a supplement in 1977 praising this fictional resort, its two main islands (Upper Caisse and Lower Caisse), its capital (Bodoni), and its leader (General Pica). Intrigued readers were later disappointed to learn that San Serriffe (Sans serif) did not exist except as references to typeface terminology. (This comes from a Jorge Luis Borges story.)

DT Day: In 2008 fliers were handed on Brigham Young University campus, saying that the last in a series of dorm buildings being torn down was scheduled to be imploded on April 1. Hundreds of people eagerly turned up to see the implosion, but to their consternation it never happened. The culprits of this prank remain unknown.

Decimal time: Repeated several times in various countries, this hoax involves claiming that the time system will be changed to one in which units of time are based on powers of 10.

Smell-o-vision: In 1965, the BBC purported to conduct a trial of a new technology allowing the transmission of odor over the airwaves to all viewers. Many viewers reportedly contacted the BBC to report the trial's success.[17] In 2007, the BBC website repeated an online version of the hoax.

Tower of Pisa: The Dutch television news reported in the 1950s that the Tower of Pisa had fallen over. Many shocked people contacted the station.

Write Only Memory: Signetics advertised Write Only Memory IC databooks in 1972 through the late 1970s.[20]
The Canadian news site, bourque.org announced in 2002 that Finance Minister Paul Martin had resigned "in order to breed prize Charolais cattle and handsome Fawn Runner ducks."

By radio stations
BBC Radio 4 (2005): The Today Programme announced in the news that the long-running serial The Archers had changed their theme tune to an upbeat disco style.

Death of a mayor: In 1998, local WAAF shock jocks Opie and Anthony reported that Boston mayor Thomas Menino had been killed in a car accident. Menino happened to be on a flight at the time, lending credence to the prank as he could not be reached. The rumor spread quickly across the city, eventually causing news stations to issue alerts denying the hoax. The pair were fired shortly thereafter.

Phone call: In 1998, UK presenter Nic Tuff of West Midlands radio station Kix 96 pretended to be the British Prime Minister Tony Blair when he called the then South African President Nelson Mandela for a chat. It was only at the end of the call when Nic asked Nelson what he was doing for April Fools' Day that the line went dead.

Jovian-Plutonian gravitational effect: In 1976, British astronomer Sir Patrick Moore told listeners of BBC Radio 2 that unique alignment of two planets would result in an upward gravitational pull making people lighter at precisely 9:47 a.m. that day. He invited his audience to jump in the air and experience "a strange floating sensation." Dozens of listeners phoned in to say the experiment had worked.

"National Public Radio" Every year National Public Radio in the United States does an extensive news story on April 1. These usually start off more or less reasonably, and get more and more unusual. A recent example is the story on the "iBod" a portable body control device. In 2008 it reported that the IRS, to assure rebate checks were actually spent, was shipping consumer products instead of checks. It also runs false sponsor mentions, such as "Support for NPR comes from the Soylent Corporation, manufacturing protein-rich food products in a variety of colors. Soylent Green is People."

Three-dollar coin: In 2008, CBC Radio program As It Happens interviewed a Royal Canadian Mint spokesman who broke "news" of plans to replace the Canadian five-dollar bill with a three-dollar coin. The coin was dubbed a "threenie", in line with the nicknames of the country's one-dollar coin (commonly called a "loonie" due to its depiction of a common loon on the reverse) and two-dollar coin ("toonie").

U2 Live on Rooftop in Cork: In 2009 hundreds of U2 fans were duped in an elaborate prank when they rushed to a shopping centre in Blackpool in Cork believing that the band were playing a surprise rooftop concert. The prank was organised by Cork radio station RedFM. The band were in fact just a tribute band called U2opia.

Country to Metal: Country and gospel WIXE in Monroe, North Carolina does a prank every year. In 2009, midday host Bob Rogers announced he was changing his show to heavy metal. This resulted in numerous phone calls, but about half were from listeners wanting to request a song.

Cellphone Ban : In New Zealand the radio station the Edge's Morning Madhouse enlisted the help of the Prime Minister on April 1st to inform the entire country that cellphones are to be banned in New Zealand. Hundreds of callers rang in disgruntled at the new law.
By television stations

In 1962 the Swedish national television did a 5-minute special on how one could get color TV by placing a nylon stocking in front of the TV. A rather in-depth description on the physics behind the phenomena was included.

After over fifty years, the 1957 BBC report of the purported bumper annual spaghetti harvest (see Spaghetti trees above) remains one of the most successful TV hoaxes of all time.
In 1980, the BBC reported a proposed change to the famous clock tower known as Big Ben. The reporters stated that the clock would go digital.

The Trouble with Tracy: In 2003, The Comedy Network in Canada announced that it would produce and air a remake of the 1970s Canadian sitcom The Trouble with Tracy. The original series is widely considered to be one of the worst sitcoms ever produced. Several media outlets fell for the hoax.

In 2004, British breakfast show GMTV produced a story claiming that Yorkshire Water were trialing a new 'diet tap water' that had already helped one customer lose a stone and a half in four months. After heralding the trial as successful, it was claimed that a third tap would be added to kitchen sinks, allowing customers easy access to the water. Following the story, Yorkshire Water received 10,000 enquiries from viewers.

In 2006, the BBC reported that the door to No. 10 Downing Street, the official residence of the Prime Minister of the United Kingdom, had been painted red. They showed footage of workmen carrying a red door. Red was the official colour of the political party which formed the government at the time. The same story was also reported in the British newspaper, The Daily Mail which credited the new design to April Fewell. The door is in fact black.

In 2008, the BBC reported on a newly discovered colony of flying penguins. An elaborate video segment was even produced, featuring Terry Jones (of Monty Python fame) walking with the penguins in Antarctica, and following their flight to the Amazon rainforest.

On Comedy Central, the creators of South Park aired a fake episode of Terrance and Phillip titled "Terrance and Phillip in Not Without My Anus" instead of running the season premiere which was supposed to reveal the father of Eric Cartman. This caused angered fans to write about 2,000 complaints to Comedy Central in the week following the broadcast. The incident was parodied in the Season 13 episode Eat, Pray, Queef, the first episode to broadcast on April Fool's day since the incident.

By magazines, newspapers, and books

George Plimpton wrote a 1985 article in Sports Illustrated about a New York Mets prospect named Sidd Finch, who could throw a 168 mph (270 km/h) fastball with pinpoint accuracy. This kid, known as "Barefoot" Sidd[hartha] Finch, reportedly lear to pitch in a Buddhist monastery. The first letter of each word in the article subhead spelled out the fact of its being an April Fool joke.

Lies to Get You Out of the House: In 1985, the L.A. Weekly printed an entire page of fake things to do on April Fools' Day, by which hundreds of people were fooled.

Comic strip switcheroo: Cartoonists of popularly syndicated comic strips draw each others' strips. In some cases, the artist draws characters in the other strip's milieu, while in others, the artist draws in characters from other visiting characters from his own. Cartoonists have done this sort of "switcheroo" for several years. The 1997 switch was particularly widespread.

Coldplay to back the Tories - On April 1, 2006 the UK Guardian journalist "Olaf Priol" claimed that Chris Martin of rock band Coldplay had decided to publicly support the UK Conservative Party leader David Cameron due to his disillusionment with previous Labour Party prime minister Tony Blair, even going so far as to produce a fake song, "Talk to David", that could be downloaded via the Guardian website. Despite being an obvious hoax, the Labour Party's Media Monitoring Unit were concerned enough to circulate the story throughout "most of the government".

President Barack Obama pulls fundings for NASCAR - On April 1, 2009, on the heels of the auto industry bailout, Car and Driver claimed on their website that President Barack Obama had ordered Chevrolet and Dodge to pull NASCAR funding. The article was removed from the website and replaced with an apology to readers, after upset NASCAR fans protested on the Car and Driver website. Conservative pundit Ann Coulter notably fell for the joke.

The Guardian to publish to Twitter: On April 1, 2009 The Guardian announced that it would be the first newspaper to publish exclusively on Twitter. LamePro - Video game magazine GamePro once featured a gag section entitled "LamePro" in its April issues, featuring joke videogaming articles and reviews. The practice was abandoned after a magazine redesign in 2007.

Game Infarcer - Video game magazine Game Informer publishes a parody of itself called Game Infarcer in every April issue. Despite making no attempts to disguise the fictitious entries, even marking every page involved with the word "parody" at the bottom, there are always letters in the May issue by readers who believed the content to be real.