While I have always taken my mother's word for it, I will take that man's word as Gospel!
What you said about your mom’s experience completely matches what this man said, too. She was the public Jackie O with those she thought were “on her level” and a nasty nightmare to those who she perceived as “below” her.
As Dave Barry says, “A person who is nice to you, but rude to the waiter, is not a nice person.”