Why do girls always like wrong guys?

Okay my girlfriend likes this other guy who's selfish, stuck up and basically thinks he's the absolute bees knees, I don't mean to generalize here but I've been noticing this type of thing with girls my whole life, so please don't get offended, if you are, don't answer this question, so why girls are you continuously attracted to complete b@stards because some of them aren't even great lookers, by the way I know you actually do want to be with someone nice but you all I even notice from my friends who are girls have this soft spot for these absolute w@nkers, I'd just like to know why?