I'm not sure. I think it has more to do with individual personalities than gender though.
I think this, too.
I don't think women are more vindictive. Rather, because they often don't have brute strength and testosterone on their side, they tend to be sneakier about how they exact vengeance, and that may come off as more vindictive. Whereas guys tend to be really up-front, in-your-face "let's get this over with" with their anger, many women tend to avoid aggressive scenarios and so they resort to a more behind-the-scenes aggression that often includes bringing other people into the situation and basically creating a lot of drama. That's just my opinion ba<x>sed on years of observation within my own social groups.
I think men can be passive/aggressive individuals and that stinks too. No, women and men can be equally vindictive - they tend to express it in different ways.
Personal experience. Women are more jealous and vindictive.
Not sure, but women are harder on eachother than the men are.