#5. Diana Payne
How hot was it when Nate had goodlooking sex with an older woman? I actually don't think Blair and Diana were enemies per se, but they had sex with two of the same guys and I don't know about you, but that's enough for me to put another chick on my shit list. Don't act like you're above that! Diana is also what Blair probably would've become had she not met Chuck. So yeah, it stands to reason that they would hate each other.