My initial 'real' motivation came from guys in my high school that were obviously really cocky and douche (arent they all at that age?) They said "The only person I guess I'll be beating is her (me)" because I had begged my way into the teacher letting me join his Male Fitness class for the semester, I was full on prepared to own those guys going in. I don't half-ass it, it's all or nothing. I love when people tell me I cant do something because it such great motivation and when I do it better the look on their faces is priceless. These guys are like twice my size and weigh easily 50% more than me but I always came in top 3 in any kind of cardio if not first and at the end of the year who got the only one Fitness award and scholarship? Me.
The best way to get back at anyone is not living a good life, it is having a sexy, hot body that says it all ;).