"An eye for an eye only ends up making the whole world blind." -Mahatma Gandhi
I've always believed in being good to people regardless of if they have been good to you or not. If another person treats you with unkindness, disrespect, speaks poorly of you, or harms you in any way: that isn't about you. That is an innate conflict they are dealing with. Have empathy while recognizing this, and send love and understanding in their direction. You're probably thinking, that's SO hard...and I agree. It is hard to do sometimes depending upon the severity of the emotional or physical pain they inflicted upon you and it is hard not to be angry and have animosity towards people who treat us wrong, but if we seek vengeance there will always be this cycle of hatred and negativity. Address the internal pain they are going through and find the strength to forgive and let go. Free yourself of the pain and put positive energy into the world. We won't get anywhere by treating an unkind act with another unkind act, we must break the cycle and only respond with love and benevolence.