Not a guarantee of course, but I think if you can't steelman your opponents, have never gone into something with some hypothesis or bias and ultimately proved it wrong/insufficiently supported and accepted that, or wouldn't be willing to specify what evidence would be sufficient for you to change your mind (however unlikely you believe that to be), you're more likely to be Homer.

I feel like there are clear signs, but either people have cognitive blind spots or are just obstinate. For example, you hear people complain that they've been for a bajillion interviews and still don't get hired (hint: the problem is you), or they're always single even though they go on countless dates (hint: the problem is you) or they're overweight and can't lose weight no matter what they try (hint: the problem is you). Maybe an inability to introspect yourself in an objective way? Maybe a deep seated belief that the problem cannot actually be _you_, it must be an external factor, so you seek that. Maybe you're not being gaslit, maybe the ever-present smell of shit really does emanate from under your shoe.