Mine's gotta be the massively scoped Patriot Movement. A brief rundown:

• The entity which is considered the government of the United States is in fact a corporation established in 1860something.
• There is a real you and a fake you which is your name spelled with capital letters. The banks and Corp. US can only interact with the fake you.
• The Corp. US has been under martial law since the Civil War, you can tell because the flags in government buildings have gold tassels or something.
• Alaska and Hawaii weren't approved by the US, just the Corp. The true US has only 48 states.
• There are a bunch of forms you can file with which you can sneak your way out of the system (depatriating/repatriating, land grants, something involving the universal commerical code).

It kinda almost makes sense as an allegory or something, but people believe these things exist.