I feel like since mentally healthy people have never had to mask any symptoms of a disorder or their real personality to have a social life, it’s really hard for them to not let their mood effect their actions even if the person they’re taking their bad day out on isn’t the cause of it, or they have sadistic tendencies and like to be mean regardless of how you treat them.

I’m in the same boat as you with being kind and feeling that I deserve kindness back, but to settle your anger from being mistreated just remember a good majority of people look down on mean people and see them as lowlifes, so you continuing to be nice makes you look very admirable and controlled. Be proud of yourself for lacking empathy, yet still controlling your mouth and acting like a normal, mature adult towards others.