Mindfuck is a neologism of sorts that probably would not be around had it not been for the Internet. The word is technically a noun, to describe something that will mess with the user's mind, but it can also be used as a verb to mean the act of doing so.

The scope of the word is broad. A horror movie that has the viewer jumping at shadows afterwards is a mindfuck. So is the Illuminatus trilogy, which blends true information with imaginative fiction until the reader doesn't know which is which. (One plot strand in the Illuminatus! books themselves is "Operation Mindfuck", a plot to spread alarm and confusion). So is the largest plot twist of Fight Club.

See also: Psyops