The Conspiracy: Ferris Bueller is a figment of Cameron’s imagination.

The Evidence: Though this theory may actually make the most sense, the evidence is the sparsest. Essentially, the evidence rests on Bueller exhibiting every quality that Cameron is lacking, essentially being the perfect version of Cameron (according to Cameron). Cameron himself is a depressed, introverted loser. It also becomes apparent that although Ferris makes all these outlandish claims, lies and actions, Cameron somehow winds up dealing with all of the consequences. Very Fight Club-esque if you think about it.