Be kind to everyone around you. This covers not using hostile language that might upset anyone.
It is an act of kindness, nothing more or less, to not react with hostility if someone else is unkind. Save most of your anger for when you are in private. In the public situation, ignore the unkind person, or if you can find an example-setting moment, kindly correct them (ex: “Disabled people have a hard enough time as it is, so let’s not use that word, ok?”)
How kind should one be with a child rapist or mass murderer?
How kind should one be with someone who spends his days facilitating terrorism?