So what are you trying to say there? That my black mate calls his half-caste son a half-caste in an attempt to insult him on the sly?
No Stevie, I'm suggesting that your mate's scale of acceptable things to say within a family context might not mirror everyone else's, so out of consideration for other people's feelings it might not be terribly polite to adopt it in public as your own to be applied in all situations.
The term "half-caste" can be extremely offensive to large numbers of people, so to avoid causing unnecessary upset to people you don't know it might be more pleasant to use the term "mixed race" (for instance), which does not have quite the same capacity to offend, as far as I am aware. It has the same number of syllables, so shouldn't cause you undue inconvenience in spoken communication, an unambiguous meaning and would probably cause fewer silly cows to moan at you.
Win-win!