The Amityville Horror by Jay Anson and the Lutz Family (1977): The Amityville Horror was a hoax that most people don't realize was a hoax because of all the movies and sequels and books claiming to be "based on a true story."
Basically, it appears as if the Lutz family and the lawyer for the mass murderer who lived in the house before them cooked up a story of a haunting -- the lawyer in order to get a new trial for his client (and to make money from a book), the Lutz family to get out from under the crippling mortgage that had made them house-poor. In the real world, the day after the Lutzs reportedly fled the house for good thanks to demonic forces, they returned to...hold a garage sale.
So it goes. The Amityville Horror is, then, an amazingly successful hoax. That it's ineptly imagined and written is beside the point.
But the ineptness does makes it weirdly endearing. The Devil, in the Amityverse, has a Swiss Army Knife of malign powers, the most hilarious of which is 'Invisible Late-Night Marching Band.' He also makes prank phone calls, summons up flies, disguises himself as a giant robed figure and a giant red-eyed pig, gropes people, slams doors, opens windows, tears down front doors and garage doors, fills rooms with the smell of poop, threatens people with a ceramic lion, causes green goo to ooze out of keyholes, summons thunderstorms, levitates sleeping people, loosens the wheels on cars, and generally makes a nuisance of himself.
Anson's pronounced tendency to throw in everything and the kitchen sink leads to a breathless description of how someone showed up at the Lutz's door claiming to be a neighbour welcoming them to the neighbourhood. He had a six pack with him. But he was too poorly dressed to be from the neighbourhood...and then he left, TAKING HIS SIX PACK WITH HIM. And he was never seen again!!!
I want a book about that guy. Was he the Devil? Was he drunk? Where did he come from? Where did he go? Oh, well. Recommended because it's hilariously bad and ridiculous.