You shouldn't waste your time talking and spending time with stupid people, so you should learn to immediately identify such individuals.
The advantage is that you can roughly determine the IQ during the first conversation.
Stupid people have read few books in their lives and have not developed their brains. Therefore, speech is the first sign of stupidity. If a person has difficulty constructing sentences, uses only simple constructions and often makes mistakes, then we are unlikely to have an intelligent interlocutor in front of us.
Smart people are always consistent and logical in their judgments because they see connections and are able to formulate their own thoughts.
A stupid person is not capable of this: his arguments always come down to faith and convictions, but not to facts.
Stupid people may listen to you in a dialogue, but they are unlikely to hear you. They are simply waiting for their turn to speak. Therefore, their remarks may sound as if they did not listen to you.