"There are several explanations for the origin of April Fools' Day, but here is the most plausible one. April 1st was once New Year's Day in France. In 1582, Pope Gregory declared the adoption of his Gregorian calendar to replace the Julian calendar and New Year's Day was officially changed to January 1st. It took awhile for everyone in France to hear the news of this major change and others obstinately refused to accept the new calendar, so a lot of people continued to celebrate New Year's Day on the first of April - earning them the name "April fools." The April fools were subjected to ridicule and practical jokes and the tradition was born. The butts of these pranks were first called poisson d'avril or "April fish" because a young naive fish is easily caught. A common practice was to hook a paper fish on the back of someone as a joke. This evolved over time and a custom of prank-playing continues on the first day of April."
In the time of Louis XIII of France, the Prince of Lorraine was held prisoner in a castle alongside the river Meuse. He escaped and tried to swim accross the river. Normally he would have been caught by the gards in boats, but a sudden and late frost had frozen the Meuse, and the boat could not continue the pursuit, and the Prince escaped. It happened on april 1st. Since that event the gards were called "gards of the fish".
British folklore links April Fool's Day to the town of Gotham, the legendary town of fools located in Nottinghamshire. According to the legend, it was traditional in the 13th century for any road that the King placed his foot upon to become public property. So when the citizens of Gotham heard that King John planned to travel through their town, they refused him entry, not wishing to lose their main road. When the King heard this, he sent soldiers to the town. But when the soldiers arrived in Gotham, they found the town full of lunatics engaged in foolish activities such as drowning fish or attempting to cage birds in roofless fences. Their foolery was all an act, but the King fell for the ruse and declared the town too foolish to warrant punishment. And ever since then, April Fool's Day has supposedly commemmorated their trickery.
Funny there seem to be a fish theme involved.
Arguably the best media-generated April fools' joke dates from a Richard Dimbleby "news report" aired on 1 April 1957 on BBC's Panorama. It opened with a line about Spring coming early this year, prompting the spaghetti harvest in Switzerland to be early, too.
Against a video backdrop of happy peasant women harvesting spaghetti from trees, whimsical claims about the foodstuff's cultivation were made in a straightfaced manner. Spaghetti's oddly uniform length was explained as the result of years of dedicated cultivation. The ravenous spaghetti weevil which had wreaked havoc with harvests of years past had been conquered, said the report.
More than 250 viewers jammed the BBC switchboard after the hoax aired, most of them calling in with serious inquiries about the piece — where could they go to watch the harvesting operation? Could they buy spaghetti plants themselves? (For those anxious to try their hand at homegrown pasta, Panorama producer Michael Peacock offered this helpful hint: "Many British enthusiasts have had admirable results from planting a small tin of spaghetti in tomato sauce."😉
http://www.snopes.com/holidays/aprilfools/origins.asp
Another good one was from comedian Alan King. In the 60's, he had an obnoxious neighbor who was contantly regaling King with stories of the great gas mileage he was getting from his Volkwagen.
The first phase of his prank had King sneaking over to the neighbor's driveway at night, adding fuel to the tank. The neighbor was going hundreds of miles without going through any gas--- or so he thought: a miracle car.
For the next phase of the prank, King would again sneak over to the neighbor's car at night, but this time, siphoning gas out of the tank. The poor guy couldn't drive four blocks without running out of gas. Drove the neighbor crazy.