When you dislike someone so much that anything they do, no matter how minor or inoffensive, annoys you beyond any rational level - exemplified by the sentence "look at that bitch eating crackers like she owns the place".
"I can't help it she just drives me nuts, she'smy Bitch Eating Crackers."
A bitch eating crackers is someone (male or female(but usually female)) who no matter what they do like eating crackers pisses you off. Usually has a low IQ or intelligence. Other versions of the phrase include Bitch eating chicken.
Person 1: Hey what's that girl's name over there?
Person 2: doesn't matter bro, you don't want that. She's a dumb bitch eating crackers