10. The Moon Isn't Real
Sometimes boring, only slightly crazy conspiracy theories just aren't enough for certain people. Going above and beyond the usual 'fake Moon landings' proposition, there is a small group of people that's totally convinced the entire Moon is a fabrication. The general theory appears to be that there is something behind the 'Moon', but what we see is actually just a giant hologram.
The proposed reasoning behind this giant Truman Show-esque illusion doesn't seem to have been formulated yet, but apparently it's powered by a massive electrical system. This theory doesn't even make much of an attempt to explain when this hologram came about, or if there ever was a real moon. The terrible video below purports to demonstrate an error in Moon hologram's imaging, so judge the likelihood of this conspiracy for yourself.