This is one of my favorites. I guess because I'm just ornery enough to enjoy watching other people's confusion when I am kind (overly kind) while they are being butt-heads. I feel it is my duty to aggravate the crabby people with kindness so that way when they are complaining about their day, they may recall; someone smiled at them. Some one gave them a drink.
Romans 12:20 tells us "If your enemy is hungry, feed him; if he is thirsty, give him something to drink; for by doing so you will heap burning coals on his head."
In being kind to others in the face of their unkindness, show a gentle heart. This verse does not imply that we are hoping bad things (hot coals) will come to this person, but the hope is that they will feel shamed from acting so mean to someone who obviously didn't deserve it and repent from the "attitude."
We don't know what kind of day each person is having and it's unfair of us to judge someone's entire personality based on a quick assessment or a few minutes in passing, so be kind. Maybe they don't realize they are being so contrary.
For others that it seems to be a lifestyle of curmudgeon, maybe their life is harder or more sad that we could ever know.
... or... they could just be mean. Who knows. But show kindness to them anyway, so that even if the rest of the world mirrors back what they give, you can be the exception and show them what a true kind spirit looks like... It looks like heaping coals.
Elizabeth Bourgeret is a life coach, author and she is the creator of the teen life skills event called Total Truth Workshop and the Leading With Love Series of books, workshops and coaching.