The Third Wave was a classroom experiment in mob mentality and it revealed some troubling things about it. The same things that are what is so wrong with extreme fandoms today.
There was a novel based on this experiment and a film made in 1981.
Here is the film in two parts, with IMO a bit better sound.
The experiment came about because the teacher, Ron Jones in real life, Ben ross in the fictionalized book/movie, could not sufficiently answer the question posed by one of his students, as to how so many citizens of Germany could claim they never knew about the evils of the nazi regime as they were being carried out all around them.
The experiment taught them why, revealing that with the right kind of stimuli and incentive, not even they were immune to the spell of collectivism.
The Third Wave really happened, but it was only a five-day experiment that the teacher and administration halted once they saw things were getting out of hand.
There seems to be no one able or willing to put a stop to the wave now, and it is no longer an experiment, but a plethora of obsessive fandoms and other subcultures gone amok.
Examples:
Bronyism, My Little Pony Fanaticism
Anti-fandom, Trolls and Fandom Wars