Is there a master list of all the incidents that later turned out to be hoaxes?
Good idea. I nominate nickcarraway. Start a thread, then as everyone posts links or memories of hoaxes in recent years you can enter them into a spreadsheet with various fields that can be sorted based on date, location, cause, prosecuted or not, etc. etc. Then every once in a while you can post the larger list as it grows.
Here's a link to start the hoax thread.