How old are you when you start to realize that some folks out there just looovve to pull a fast one? What is that makes pranks, cons, rip-offs, and good 'ol hoaxes so darn fascinating? We can read up on them for hours in our household. And if the grown-ups try to pull the book away from you, just let them know that hoaxes help you learn to think better: it teaches scientific method and the search for a proof.
In stepping into the swamp of hoaxes, a good place to start is The Museum Of Hoaxes (aka Unnatural Mystery). I wish there was a ten story version on my block.
Although some might tell you otherwise, Nessie, the Loch Ness Monster has to rate at the top of the all time list. She's even got her own website.
And a couple of good commercials exploiting her existence (not).