Ok I really need someone to help me! (CONTINUED)?

So my friend has another friend called Jessica. Jessica is like socially awkward, she's really rude to me all the time and like never includes me in anything. Pretty stupid right? But the thing is tomorrow is her formal so i'm going with my friend. Jessica is my friend's best friend and when i tell my friend if she' rude to me i'll b**** her out, she gets pissed. If Jessica acts all snooty and like too good for me attitude, what should i say to not cause a fight? Because honestly this is soo stupid. Thanks (: