Runetrails
It will probably shock people to hear that the entire ‘chemtrails’ thing has a fragment of a flicker of a technicality of a smidgen of a basis in reality. Sort of. Well, not really, but there is a tiny grit of truth out there that was later turned into a nacreous sphere of conspiracy theory. And this was encouraged, too, on the sensible grounds that there’s nothing like a conspiracy theory to hide an almost, but not quite, unrelated actual conspiracy.