Like not some shit you saw on the internet half-ironically, but something an actual flesh and blood human said to your face in a real physical space.
I'll start. I was working a service job and I had just finished helping this dude find what he was looking for. Seemed like a normal middle aged guy. After I showed him the product he need he looked me dead in the eyes and went "you know kid all the National Parks have secret bases in them." I just nodded, at first figuring maybe this was some actual real shit, like it wouldn't surprise me if the US military actually did hide some hardware or whatever in the National Parks. "They're filled with Samurai", uh, okay? "You see Japan actually won WWII, no bombs were ever dropped. And now the Samurai have secret radio bases in every National Park, Alcatraz is their headquarters." I decide to just fucking leave at this point and race walk to the back of the store and hide in the managers office. Apparently the dude spent 15 minutes wandering the store looking for me and asking my coworkers where I had gone.
The term "conspiracy theory" was created by Karl Popper and utilized by US intelligence to discredit people from pointing out the actually proven and declassified things done by US intelligence.
The idea of the ‘conspiracy theory’ was developed by the anti-Communist philosopher Karl Popper in his 1945 The Open Society and Its Enemies. Popper was against the view that war, unemployment, and poverty were the ‘result of direct design by some powerful individuals and groups’. Theories of society – such as Marxism – which attempted to understand the social mechanisms of war and unemployment could be softly dismissed as merely conspiracy theories. Popper pointed out that conspiratorial groups were paranoid and – like Nazism – would lead to totalitarianism and genocidal policies. Popper’s liberals viewed any left-wing criticism of the US state and society as conspiratorial; the actual conspiracy theorists – such as Joe McCarthy and the John Birch Society – were sniffed at, disparaged, but not taken seriously (after all, as Daniel Bell wrote, the Communists – unlike the John Birch Society – had a conspiracy that ‘was a threat to any democratic society’). This was not a principled objection to conspiracies, but a class attack on any criticism of capitalism and imperialism.
The idea of the conspiracy theory was used to de-legitimize genuine investigation of covert behavior by the government. Implicit faith in the goodness of US power generated the view that the US government would never use illegal means to secure its ends, and that if there was any suggestion that the US had fomented a coup – that suggestion was dismissed as a conspiracy theory.
For example, those who suggested that the US/United Fruit perpetrated a coup against the Jacobo Árbenz government in 1954 would be roundly mocked as conspiracy theorists. Later, when the documents proved that the critics had been correct it was too late.
"Weird" conspiracy theories like pizzagate, Qanon, Flat Earth, Large Hadron Collider being a gateway for Shiva, Finland not existing, lizard people, ancient aliens, etc. are a mixture of pop culture nonsense, antisemitism, sincerely held quasi-religious beliefs, and strawman conspiracy theories deliberately seeded by US intelligence to resemble and discredit more reasonable theories that actually align with historical materialist thought.