Why am I so vindictive?

I don't consider myself a bad person at all. However, when I feel somebody disrespects me in one way or another, I have an almost compulsive need for revenge. I remember every insult/disrespecting remark people make and swear to myself I will get them back at least twice as hard. I will usually act like I dont care what people think/say of me, and put great effort in staying anonymous while getting my revenge .

At this very moment im planning to get revenge on a girl because I really, really like her but she doesn't seem to like me back. For me this is enough reason to get revenge on her. I just have to make her pay for not liking me, even though shell never realize it was me who did it.

My question is simple: whats the psychology behind this?