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.
I live in Colorado, where there's a bunch of conspiracy theories surrounding the Denver airport and its underground baggage handling system. One of my old co-workers said that there were secret tunnels connecting the airport to various military bases in the area, including Cheyenne Mountain and Area 51 (which is like 700 miles away). The same guy claimed that the Aurora movie theater shooting was coordinated by rival film studios to ruin the premiere of the Batman movie.
Another co-worker at another job believed basically every conspiracy theory you can think of: Qanon, flat earth, new chronology, 5G causes coronavirus, vaccines contain microchips, etc. As near as I could tell he wasn't anti-Semitic, or at least he hid it well. I sometimes listen to Qanon Anonymous so occasionally I'd egg him on if I was bored, but it got tedious and a little sad after a while.