The spaghetti-tree hoax was a three-minute hoax report broadcast on April Fools' Day 1957 by the BBC current-affairs programme Panorama, purportedly showing a family in southern Switzerland harvesting spaghetti from the family "spaghetti tree". At the time spaghetti was relatively unknown in the UK, so many British people were unaware that it is made from wheat flour and water; a number of viewers afterwards contacted the BBC for advice on growing their own spaghetti trees. Decades later, CNN called this broadcast "the biggest hoax that any reputable news establishment ever pulled".
"The Space Needle collapsed." -- Those were the words from the KING 5 Newsroom which aired live on April 1, 1989, that launched perhaps the most infamous April Fools' Day prank in Seattle history and sent many in Washington state into a panic.
Many people did not get the joke, even though after the "news bulletin" was over, a local comedy TV show started. I guess it is alright to fool people, but not alright to fool and scare them.
The spaghetti tree hoax gets my vote for best April fools day prank. Do you have any favorite April fools day pranks you would nominate?