We should never allow ourselves to shrink from standing for what’s right with the excuse of trying to “help” that other person, or out of a desire not to “hurt their feelings”. Bad behavior is just that, it’s bad. We can’t allow ourselves to be treated badly or taken advantage of as it doesn’t just hurt us; it also hurts the person committing the bad acts. By standing for what is right we both set an example for the other person as well as teach them that they must behave differently if they are to be part of your life.
Finally, we have to recognize when the time has come that we must simply walk away. At the point it becomes clear to you that these petty or mean spirited people are not going to change, the best thing to do is to walk away and cut off any association with them going forward. As hard as that may be, there comes a point where that may be the best option. My suggestion is that this step be taken only after you have taken time to truly contemplate if doing so is the right thing for you to do.