I have a friend with a one year old that bites people, maybe as a sign of affection, but doesn't know that it hurts others. How can his parents discipline him regarding this behavior? Do you try to show him that his actions actually hurt others?
Whatever you do, don't bite him back to show him that it hurts. By doing that, you'd demonstrate that other people bite too.
He likely doesn't know that his biting hurts people, but their reaction to being bitten should teach him that. If someone bites me, I would clearly and loudly say Ow, that hurts! and then move away from and avoid interaction with the child. The idea would be a subtle, passive punishment by way of not giving him attention, because attention equals encouragement. Instead of moving myself away, I could also (if it's my kid) move him away, e.g. put him in his crib and leave him alone for a (very) short while. It's a simple time-out.
Given more context perhaps a more useful answer can be provided, so please edit the question to add more information.
Is he still teething? Babies tend to bite things as their teeth are coming through, as it helps with the utterly weird sensation of something forcing its way out from inside their jaw.
My friend's 6-month old tends to do this a lot, and they're concerned that he may continue after the teeth have come through, especially as while he's got no teeth, it's just adorable, so he's getting a certain amount of positive reinforcement when he does it.
One thing that might help is some form of teething ring that he can chew on.
If he already has something like this or he's past the teething stage, then it may be that he's picked up that it's a good way to get attention, in which case, what Torben said.
We always lightly bopped our kids on the mouth, therefore showing him that his mouth is what hurt you. Then say No, we don't bite people in a strong forceful voice. The child will learn quickly not to bite.
The other thing to think about is what is the child trying to say. It is an age appropriate, although not allowed, behavior for children that have something to say but no words to say it. If you can figure out what he is trying to say after the above you can say it for him. For example, 'No, we don't bite (in a forceful voice and then in a regular voice continue) instead say: I don't like it when you grab my toys'. No, your child will not necessarily know what you are saying but I have always been an advocate of the idea that we don't know when children start understanding so speak to them as if they do.
Simply this... Wherever their target is, place a yucky-tasting substance on it. My son always bit my shoulder until one morning I rubbed pea soup (he hates peas) on my shoulder before I lifted him up out of his crib. He bit, and sure enough, he spat and scowled for 5 minutes. I continued this every day. He was cured from biting in a week.