Bite him back. Hard — not hard enough to break skin or anything, but hard enough to make him wince or cry.
Then ask him how he feels. Ask him if you made him angry, or hurt, or what. Ask him if he thinks you feel that way when he bites you. Explain to him that when he bites you, it hurts, it makes you sad, and it’s not fun.
At the early ages, you can’t try to rationalize with a pre-rational being. You have to frame the behavior in terms that are real and tangible to him. Things that he has solid understanding of. Also important is a strong amount of immediacy.
You shouldn’t have to do this routine more than 4-5 times before he “gets it.” It’ll also help him develop empathy for other people’s feelings which is important both for his own development of self and identity along with the realization and understanding that other people outside him also have feelings, even if he can’t feel them directly.
Good luck, Kevin. It’s a long, strange trip …