Since when is it justified to hurt another person because you have been hurt yourself? Two wrongs don't make a right, and it fixes nothing. It has no good reason. But as humans, we seem to have this need to hurt others because we were hurt. We say "It will never happen again", and then make the same mistake someone else made to us. Nit-picking at another persons faults so we have an excuse to do it. Totally ignore their strengths, and the fact that they are human too, and have probably been hurt as well, and we just added to that pain out of selfishness. I can see it because I've caught myself starting to do it, and some times done it. I'm not exempt from it, and neither is anyone else. I think being mindful if it a step in the right direction. It is definitely hard to not lash back when attacked, or wronged in some other way, it's almost an instinctual reaction.
And it stings that much more when you were being nice and just trying to connect with some one, and they not only knife you in the back, but give a twist to make sure you knew it was there. And then they make like they are better than you cause they did it. In that instance, it's understandable to want to lash back, I don't think anyone would dispute that. But they made their choice, even if it was a bad one. It's hard, but they made it obvious they aren't worth the energy to try to strike back, they will just do it again. They will probably remain alone, because they can't see they are their own worst enemy. They can't see what is happening, all they know is there own pain, and feel the need to judge and attack anyone that gets close.