A list of very non-mainstream conspiracy theories that aren't completely braindead, and are at least creative or funny. I will note, as a disclaimer, that I believe none of these at all.
300 years of medieval history is fake.
Earth experiences four days simultaneously.
Nibiru (alleged celestial body) will either collide or interact with Earth, resulting in a doomsday.
Taylor Swift is lesbian (or at least bi).
Eyes emit beams that cause the sensation of vision when striking an object.
The expansion of Earth causes continents to drift apart.
Nuclear weapons don't exist.
Zheng He discovered the Americas in 1421.
The Mesoamerican Long Count calendar ends on December 21, 2012, bringing about doomsday.