The origins of the "holiday" date back to when Pope Gregory changed the calendar from the Julian to the new Gregorian Calendar we use to this date, subtracting 11 days from the year to bring the calendar back in alignment with the seasons, and moving the date of the new year from April 1 to January 1.
What we are celebrating is the remembrance of a bunch of people too dumb to realize that the calendar had been amended and the date of the new year moved back three months.
Now normally this shouldn't be too much of an issue. If people want to celebrate the base idiocy of human nature, that is their lookout. What gets me is how pervasive and invasive this so-called "holiday" actually is.
It gets to the point that no one can update a news story, no one can make a post, no one can put ANYTHING even remotely unusual up on April Fool's day without getting called out and accused of "punking" someone. (Where the heck did THAT term come from, anyway?) No matter that the post was true--any intelligent discussion about it gets debunked by people screaming "Bulls**t" because the post just HAPPENED to be placed on a date where the majority of the world decides to detach their minds from their brains and act like Jim Carrey and Jeff Davis in "Dumb and Dumber." Except they, at least, were getting paid for it and were laughing their ways to the bank.
I have opted out of this ridiculous celebration of human inanity, and will continue to do so.