You can't mention that without noting a famous hoax by H. L. Mencken. Wendy McElroy tells about it here.
The best modern-day hoaxer is probably Alan Abel:
In 1959, the Society for Indecency to Naked Animals (SINA) was formed from a $400,000 'bequest.' A movement was born which held demonstrations at the White House, threatened Greyhound Bus Lines with a boycott (after an employee was fired for painting pants on the 'naked' dog) and which claimed 51,000 members.What with some of the absurdities done in the name of animal rights, this one might work even better today.
"Naked animals everywhere...they hang their heads in shame," declared the President of the society. Four years later, the 'President' was exposed as Buck Henry, a comedy writer. The entire SINA movement turned out to be an elaborate hoax by Alan Abel. Abel later claimed the Martians landed on Long Island and placed his own obituary in the newspaper.
Want a book on hoaxes? Here's one. Honest. He has a museum too - see for yourself.