Kindness is not an act. It is a lifestyle.

Be kind to everyone, yes, even those who make it hard to be kind to them. 
I am kind for two reasons:

Most people have a hard life, and it cost nothing to make their life a little better by treating them kindly.

And second, that is part of the code that we live by.

Our actions do not depend on whether or not others are kind, honest, or live as they should; our actions are determined by our principles, our code of honour.

For me, kindness is not really an act as much as it is a part of my lifestyle, just like living with honour, character, and integrity is living according to my principles.

Live life, my way, regardless of how others live theirs.

So get out of the habit of judging others, and just be kind because that is the kind of person you have decided to be.
Make kindness a part of your lifestyle.

ps/smoh