#6. Jack Bass
Jack was more of Chuck's enemy, which makes him Blair's enemy as well. After all, if you expect your boyfriend to hate someone you hate because it's rule number one of being a good boyfriend, it's understandable why you should do the same. That being said, she probably should not have slept with Jack. He is douchebag hot, for sure, but he lorded his tryst with Blair over her head which is manipulative. So she had every reason to despise him after what he did to her. Also, while she acts like she's confident and composed, she was still just a kid when it happened. So he's more blameworthy.