This could not be more apt for the day I've had today!
I am a BIG believer in this quote, I generally try to live by the motto treat others how you'd like to be treated, though there’s many people who I've had the displeasure of crossing paths with who don't live by this and will happily give no regards to your feelings, until they need you or need you to do a favour. This bit is key because they always eventually need you for something!
I quite often try to diffuse a situation (particularly if it’s a work one where I can't say exactly what’s on my mind without being fired!) by killing someone with kindness, if they choose to act a certain way don't lower yourself to their level and be defined by their poor choice words. I find most often than not if you react in a dignified way, it only highlights further how poorly that individual has behaved and they will be too embarrassed to continue.
Hope you have a better day than me!