Have you had that experience that someone backstabbed you/hurt you so much all you wanted to do was diss them down the ground or punc them in the face? I'm sure everyone had that feeling at least once in their entire life. And I know how many negative energies can someone evoke in us if they handle us in a less than decent manner... and it would be easy to kick their butts or swear at them and insult them.
But sometimes ignoring them or being super nice is the best revenge. This is pure psychology. Those people who love bringing other people down usually feed from their outraged reactions. They get satisfaction out of see you hurt, angry, devastated - they love seeing that their deeds actually affect these poor people. Do you really wanna give them this satisfaction? No, I don't think so.
Especially if you have a person in your life who hates you for no apparent reason, and kicks into you whenever he/she finds an opportunity, being super nice is the best revenge. It's actually going to make them outraged without you turning out of yourself or steeping down to their level... or even beyond their level... because that's what would make them happy. And they could not even say anything about it, they don't have an argument.
Also, you're gonna be more optimistic and happy on the long run, if you try not to get so sensitive and captured by evil people's schemes. Just be like Pollyanna, and try to see the best in every situation. If you keep calm and col,lected, you are going to be balanced and mellow, and that's what everyone needs.