My own paranoia that the Large Hadron Collider will create a black hole that will swallow the universe is both well-documented and completely made-up. But it is by no means the wackiest theory anyone ever had about the gigantic particle accelerator lurking beneath placid Switzerland.
In 2008, Holger Bech Nielsen of the Niels Bohr Institute in Copenhagen and Masao Ninomiya of the Yukawa Institute for Theoretical Physics published a series of papers that said the LHC violated enough natural laws that it could never be operational and in fact attempts to turn it on would cause space-time ripples that would flow backwards in time and wreck the thing before it ever fully fired up.
No experiments regarding the Nielsen-Ninomiya hypothesis were ever conducted, but it was proven incorrect when the LHC did discover the Higgs Boson and did not spontaneously Tardis itself out of existence. The jury is still out, of course, on the whole black hole swallowing the universe thing.
The Nielson-Ninomiya hypothesis was always iffy, since no one has ever recorded an instance of time somehow self-correcting itself backwards and there are plenty of candidates that defy rational thinking to the degree that they should have triggered it. Nancy Pelosi winning elective office, Will Farrell getting work as a comedian, people taking Bill O'Reilly seriously, Mike Huckabee running for president twice -- any or all of these events should triggered the backwards-correction effect as the universe attempted to regain its equilibrium as a rational entity capable of being understood. So the hypothesis was never really practical.
Unless the universe isn't rational. In which case we might see something like college students arguing not for their right to see and say whatever they wished, but to be protected from seeing or hearing anything that might offend them...uh-oh.