Jenny Humphrey, Gossip Girl
Jenny was so absorbed with climbing the social ladder on the Upper East Side that she didn't care who she used or hurt in order to get ahead. Even in the first season, when she became really good friends with Eric van der Woodsen, she ditched him the moment she got a rich boyfriend. And then told Eric it was "cute" that he was jealous when he told her Asher Hornsby wasn't the guy for her — even though Eric said that because he was actually seeing Asher in secret and didn't want Jenny to get hurt. She wasn't someone you could put your trust into.