6 Answers

Smile and say how are you today, it's nice to see you.

....be a good listener 

....honesty 

ask a person about themself. People love to talk about themself......especially about their children and / or grandchildren.

If they are thinking this , for those reasons , they may be temporarily mentally disabled. There is highly likely no quick correction. Probably a hormone/physical problem that in reasoning skills. Trying to reason  to them may complicate their ability to think and futhermore assure their decision. Chances are ,they will overcome/forget about it in time.

Well, that's just odd. 

Guess you'll just have to use your straightforward, no games, nonconfrontational approach to get the problem out in the open. 

be at ease yourself.  people quickly pick up your feelings and vibrations and mood. plus I agree with what everyone else has said as well.