Do Unto Others......i believe this Golden Rule.
Most of the time I even go beyond that and I'm kind to people who are being downright ugly to me.
You never know what someone else has been going through. Sometimes people behave rude when they aren't even aware of it. There may be circumstances causing their unusual rudeness.
Other times, people are just downright rude because that's who they are.
Nine times out of ten if you show them kindess, they'll show it back to you.
If they don't, just let it go and avoid the stress of confrontations.