There's a few things I try to avoid discuss with people that I don't know.
Religion, politics, sexuality, etc.
Some people seems to be grim sometimes, but may be they're just clumsy, so you keep striving to understand that perhaps they don't act like that wilfully. Being a bit more shrewd will make you take decisions and answers aright.
But we must learn how to feel if someone is shallow while we're shaking hands, before start any conversation that results in an awkward situation, reminding that good look, nice clothes and fancy cars can't turn people smart.
They never will understand the words: - point of view -, - looking through other perspective -, or even the expression, - if I were in your shoes -. Better don't waste your time.
The constructions of good ideas will never happen, time will be wasted and everything you say or they say, will be thrown away, there will be nothing good to keep.
Moreover, if you lightly and sophisticatedly take down the pride of people like that, they will try to undervalue you, driving the conversation to be about their car and their clothes. That's the moment you know they have nothing left to say, indeed nothing left in their lives.