I usually say the following. I'm paraphrasing a spiel I have delivered in person several times and which seems to get things across.
'there's a kind of decentralized cult called rationalism. they worship rational thinking, have lots of little rituals that are supposed to invoke more rational thinking, and spend a lot of time discussing their versions of angels and demons, which they conceive of as all powerful ai beings.
rationalists aren't really interested in experiments or evidence, because they want to figure everything out with pure reasoning. they consider themselves experts on anything they've thought really hard about. they come up with a lot of apocalypse predictions and theories about race mingling.
silicon valley is saturated with rationalists. most of the people with a lot of money are not rationalists. but VCs and such find rationalists very useful, because they're malleable and will claim with sincerity to be experts on any topic. for example, when AI companies claim to be inventing really intelligent beings, the people they put forward as supporting these claims are rationalists.'