I don't let the bad manners of others dictate to me how i act around others.
Teach through example.
When I was little and out shopping with my mom, she always stayed close enough to keep an eye on me. She made sure I would hold doors for her and other people, would use
please and
thank you /
sir and
ma'am when talking to clerks and cashiers, and would offer to carry her packages. Basically, I was corrected enough times that I learned what was expected of me.
When I was about 16 or 17, I was working on a Saturday morning at this ice cream and dairy plant. The owners are rarely there for more than a quick minute on the weekends, but that morning one of the two brothers/owners was there. The plant doesn't usually operate on the weekend -- just the ice cream retail store run mostly by high schoolers. His office was in the very back of the facility, and the retail store was in the front.
An older lady called and asked to speak to my boss, so i found him at his phone lines and transferred the call.
Enough time passed that I completely forgot about the call -- nothing memorable about answering the phone. Then the owner walked in. He said the lady that called couldn't compliment me enough for my manners and customer attentiveness. This was in the early 80s, so I guess good manners and poor customer service had already begun to be the norm.
I told him that's just how i I was raised. Not sure if he realized, but my grandmother worked in the same plant with his father decades before.

Whenever i see bad manners and an empathetic attitude toward others, i just chalk it up to bad parenting. Nobody learns how to be that way. They just never learned any other way.