As far as your interactions with him in just this instance, you follow his bread crumbs into forests of fog and confusion. If he doesn't answer a question, don't let up until he does. Don't follow him onto tangents of meaningless arguments from effect. That's where he wants to go because that is where relativists like to reside. The example of the bushmen is a good one.
However, the real point of this from point of view is that he said in the other thread that he is willing to use violence against you, so I'm not sure why you continue to engage with him.
Democracy: The Newest Innovation in Livestock Management Techniques!
When people kill for a lie, they also murder the truth. - Stefan Molyneux
百聞は一見にしかず。- Japanese Proverb, "Hearing something 100 times can't beat seeing it once." The only way to spread philosophy.
People who teach their kids conclusions are harming their kids ability to understand reality, and are thus abusers. Those who teach methods are not. This is a difference in kind. People who teach their kids the conclusion that Santa Claus exists are not inflicting a lifetime full of guilt or fear. Those who teach that Jesus Christ exists are. The latter are far more egregious. This is a difference in degree.