I just wrote a post about treating people the way you want to be treated, not saying things you shouldn't and saying things you should, being the bigger person, etc.
I'm not going to post it. There was more to it than just that and I feel like in the long run, I would regret posting it for everyone to see. I'm taking my own advice.
However, I do want to say that when you have the opportunity to hurt someone, whether they've hurt you before or not, don't do it. When you are wrong and have the opportunity to admit it, learn from it. When you are right, be nice about it. If you are about to say something to someone that you're going to regret later, first think about how you would feel if someone said that to you and then don't say it. Squash it. No one can or will judge you for thinking what you're thinking but people can and will judge you for saying what you're thinking. And most importantly, don't say things just because you're: frustrated, upset, mad, wrong, or because you just simply want to hurt the person that hurt you.
That's all. Just a little food for thought.