I tried to tell my LO that biting is bad and it hurt mommy, etc, etc, but all he would do is bite harder, pull the nipple with his teeth, let go and then give me a great big smile. The one thing I've done that seems to have helped (I know this sounds so bad) is to pinch him (I read it somewhere on this forum) on the leg when he bites. He still nibbles sometimes but not nearly as bad as it used to be.