I've noticed that it's mainly women my age (50's) who never say thank you. We usually get a very nasty look like we're going to rob them or something if we hold a door etc.... I once picked up a woman's credit card that she dropped on the ground and when I went to hand it to her she snatched out of my hand. I seriously thought she was going to hit me!
I teach middle schoolers who are more polite than most adults.