What trait automatically makes you think someone is stupid?

I prefer uninformed or ignorant rather than stupid. I'd actually have to get to know a person's views and why they think that way before I come to such a rash judgement.

Honestly? When someone brings up the idea? Thus I'd say move on and forget, and interest yourself in things that bring out your best.

people who are self absorbed. think they know everything, are entitled to everything, etc.

there never the brightest people.

walking around with their mouth open. I do it myself when I don't want to get a reputation as a guy who can get things done

When I'm behind a car with a Bernie Sanders sticker stuck right on the Trunk!

Making snap judgments and assumptions about people.

They cannot spell their own name.

Yelling

Bravado

Racist people

Arrogance