Ask them how many four cent stamps in a dozen
Good opening question to ask if you find a talkety lib sitting next to you at a bar. If He can’t answer just instantly move 4 seats down.
I was at a restaurant with my ex-GF and her friend. I asked tough questions like how long does it take the Earth to spin around once? How long does it take the Earth to move around the sun once? Etc.
Both of them looked at me like I had two heads and neither had an answer.
As you can imagine conversations with the ex were pretty simplistic. Hence the word “Ex”.