A pig is someone you are dating/living with, etc, that tells u they love you and you are their world and still talks to other women in a sexual manner and also receives emails of dirty photos of the women and tells them he wants more dirty photos!
A friend that eats all your food but ensure you food for the rest of your life, a friend that is there for you at any second or time. That one friend that loves you the most.
"Hi, Sara, I justfound out Marie is a pig friend"
"Of course she is, she always eats your food but always shares hers"