You can always tell a lot about someone by whether they believe in conspiracy theories.
I agree, but I look at it like this: A small portion of them are true. Some have proven to be true - we just don't consider them conspiracy theories after they pop - they just become weird facts of history - whether we're talking about famous stuff like the Manhattan Project, Iran-Contra, or less publicized affairs like Operation Northwoods (seriously - look that up - it is like an Alex Jones wet dream).
So for me, I use a ratio to gauge. If I meet someone who seems really conspiracy-minded, I test them to see whether they're being thoughtful or reflexive. The kind of person who believes 1 or 2 conspiracy theories out of 10 is probably at least making an effort to be objective. I'll still make fun if he believes something particularly ridiculous, but true tin-hat people are notable by an
unbelievably low resistance to buying into every theory they hear. Their response to basically everything is
of course that's happening and
of course it's being covered up.
So if you run through the big list of conspiracies and see him nodding along to most of them like it's a fact of nature, you don't have to spend any more time trying to figure him out - you pretty much know where you're getting.