Extreme reasons to hate your bestfriend?

We have to do an excercise in our class and I have to come up with a reason why my best friend would be the last person i would want to see (hate). we are both female, and i would rather the reason not be because she stole my boyfriend (used to much). I just cant think of any juicy interesting reasons. The reason has to be legit and pertaining to her doing something that effects me. Ideas please!!