If you are kind only to the ones who are kind to you, and bad to the ones who 'deserve it', you will probably feel bad sooner or later, and you'll lose yourself in right and wrong, principals and judgment. To be what we are is independent of whom we are with once we reached our Self. Thus kindness and compassion are independent of whom we meet, at least under normal circumstances. I also think we can be pushed to unrecognisable extremes depending on our environment. That's why it's so important to detox your environment and seek groups and places that allow you to be You.
When how we are is independent of whom we meet, we are probably also closer to being at peace in both heart and mind. However, this is not what we are told and taught to do. In fact we are often encouraged to react to a behaviour, not as ourselves; "Go on, hit him back, don't be such pussy, punch his face, he deserves it."
Under normal pressure and circumstances how you are is not about them, him or her. It’s about you. Others might have other opinions, do differently, be mean and silly, but that’s not the point here, the point is you, and what you are to yourself. How you act, and what you say is how you are and vv. Mother Theresa said, "It’s not about him and me, it's about me and God." What changes these two ways of being is only perspective. Do you reflect You or do you reflect them?
If you swing back and forth being kind, and being mean, being open or being judgmental, depending on whom you encounter you will sooner or later split yourself in many personalities - at work I’m the sharp business woman, with my kids I'm the caring mum, with him I’m tough, with her I’m kind. Those many forms of you take you further away from your Self, until you one day don’t know who you are anymore. It’s very common, we see it all the time and we see the suffering that comes with the 'having to be' what we are not, relying on outer input all the all the time.
Being healthy is the journey back to You, a life long journey. It is as if we have censured our ‘unconscious’ awareness so that we only act on the learned conscious thinking. Getting to know yourself again reflects your own self, and implies opening up to that unconscious awareness. At our Olive retreats we use proven technics to 'find' your lost self. Some would call it letting go of the controlling mind, connecting body and mind, or being mindful. We would probably call it just being. When you see the inherited thoughts that make You, you have a more of a choice to let go and become just You.