Extreme/insane positions on everything. Not just one or two insane positions, not just political extremism; when I say everything I mean EVERYTHING. No nuance allowed. And it has to be fully sincere, otherwise you are dealing with a Jreg.
There are milder versions of this, but I have rarely met a child that didn’t have a strongly held insane belief formed from their limited experiences. My favorite was a kid who told me that eating pasta supports fascism because it comes from Italy, so loving Italian products means you support Mussolini. Pizza is fine, though, because that’s American.