To "bite the hand that feeds you" is to harm someone who has been helping you. Example: "We treat each of our customers with the greatest respect here. We never bite the hand that feeds us." If you feed an animal and it bites you on the hand you will probably not feed it again. If you forget that a person has been doing something to help you, and you harm the relationship, you are "biting the hand that feeds you". Example: "We have been your best customers for years. And suddenly you treat us so rudely? You should never bite the hand that feeds you."