Have a favorite conspiracy theory (they doesn’t pertain to recent electoral/political shenanigans)?
I’ll offer the Phantom Time Hypothesis: “The phantom time hypothesis is a historical conspiracy theory asserted by Heribert Illig. First published in 1991, it hypothesizes a conspiracy by the Holy Roman Emperor Otto III, Pope Sylvester II, and possibly the Byzantine Emperor Constantine VII, to fabricate the Anno Domini dating system retrospectively, in order to place them at the special year of AD 1000, and to rewrite history[1] to legitimize Otto's claim to the Holy Roman Empire. Illig believed that this was achieved through the alteration, misrepresentation and forgery of documentary and physical evidence.[2] According to this scenario, the entire Carolingian period, including the figure of Charlemagne, is a fabrication, with a "phantom time" of 297 years (AD 614–911) added to the Early Middle Ages.”
And - of course - “The proposal has been universally rejected by mainstream historians.”
I had a similar experience working on the Lunar Reconnaissance Orbiter and the "we never landed on the moon" nutjobs, but the Mars people are far crazier.