According to Wikipedia (I know, it isn't always the most accurate resource, but I'm being lazy today)
April Fools' Day (sometimes called All Fools' Day) is celebrated every year on April 1 by playing practical jokes and spreading hoaxes. The jokes and their victims are called April fools. People playing April Fool jokes expose their prank by shouting April Fool. Some newspapers, magazines, and other published media report fake stories, which are usually explained the next day or below the news section in small letters. Although popular since the 19th century, the day is not a public holiday in any country.
Geoffrey Chaucer's The Canterbury Tales (1392) contains the first recorded association between April 1 and foolishness.
Who knew it's been around this long. But really a who day to celebrate pranks, jokes, and overall foolishness. I think it's really all about how happy we are to see spring after a long rainy winter and then the weather does a crazy turn shouting "Ha, April Fools!"
Whatever the origin, we have a crazy holiday that celebrates the bizarre. On to the next odd thing . . .