If you want a solid reputation to follow you into single life, you'll need to learn how to break up with class without discussing the emotional vampire your ex was. Remember that despite what she's done, you still played a part in the relationship, and she's going to be out telling people about what that was like. Complaining about your ex is not exactly a turn-on when starting a new relationship, so you want to stay out of the habit now. Also, dragging up her bad qualities is just going to turn her into that emotional vampire one last time. Why would you want to do that when you can make a clean break?
Give her direct reasons for ending the relationship and not just vague feelings. Calling her an emotional vampire will just make her mad, but telling her that she talks down to you might act as constructive criticism. It's also going to keep you from being convinced back into the relationship. Try to be honest while remembering that no matter what happened between the two of you, your ex is still a person with feelings. She deserves the truth, but she also deserves to be respected.
Carefully explain yourself without adding unneeded insults. If you don't want her repeating what you say to her friends, don't say it. If you break up poorly, that's going to be the last thing she remembers about you. While that might not matter right away, it will when you and a future girlfriend run into her at the grocery store and she lets loose. You might also be dating a mutual friend or acquaintance at some point, and you don't want the word to get out that you're a mean-spirited guy who doesn't care about how the women you date feel, during the relationship or during a break-up. Once you tell her how you feel about the relationship honestly and for these reasons, you want to break up, there's no need to add "Plus, you were an emotional vampire sucking the life out of me." Save this insult for your own friends.
Treat the break-up with respect and let her share her feelings without being interrupted. Remember that she might not be expecting the bad news. As bad as she was, everyone needs time to cope. You don't have to prove that you can win the final battle. After you have your say, shut your mouth and listen for a while. She might want to scream at you, and that's okay. Keeping your cool will help you cope better in the long-run and may help keep the peace between you and your ex. Your feelings right now might be that you don't care about keeping the peace, but making an enemy out in the dating world is never a positive thing for your love life.
Get everything over with as soon as possible so that you can both go your separate ways without looking back. Unless you are a glutton for punishment, make sure that she's fully clear on the relationship being over. If you are living together, think about your exit strategy before actually breaking up. One last fight won't solve anything, and neither will making her feel bad. Rather than discussing the emotional vampire your ex was during or after the breakup, have your bags packed and arrange for somewhere to stay before you break up. Then, plan out what you want to stay carefully, let her speak and get out of there without another word.