What things do people often claim to be brilliant about without proof?

This is about people being certain about their judgement in the absence of any evidence.

My first example comes from a theater director who told me, “I can tell right away if someone is right for the part.” And I thought to myself, “What you mean is you can come to a snap decision without effort. But in casting, it’s impossible to recognize the better actor whom you dismissed at auditions.” He was sure of himself, I’ll give him that. But as we all know, being wrong and sure feels exactly like being right and sure.

Then there was some television program where one of the characters repeats the old saw, “You can tell a lot about a woman by the way she dances.” Often this is intended to mean to know how they will be during sex; and of course applies to men as well. Certainly one can draw a lot of conclusions about the person who is dancing. But we have precious little feedback to help us refine our juvenile assumptions about the link, and even if we have lots of partners whom we observe dancing first, our time with them is colored by our expectations.

Can you come up with other situations where people hold out their perceptions as being nearly infallible without ever having evidence to back it up?