How can you tell if someone isn’t bright?

This is something I wrote earlier.

It's not about catching someone out or prove you are superior, it's about minimising the time spent with 'harmful' people. I am not saying these people are trying to harm you but spending time with them can be emotionally draining and it's not good for our wellbeing. Sometimes it's good to know what we are getting ourselves into.

http://www.everydaythinker.org/2017/09/21/can-tell-someone-isnt-bright/