Aside from the reference calling someone a coconut is a great way to get them offside if they've got brown skin, so I wouldn't recommend going around saying that title in real life...
Oh yeah, it's not supposed to be a title, it's an idea
"My mother ... would give us a hard time sometimes, and she would say to us, 'I don’t know what’s wrong with you young people. You think you just fell out of a coconut tree?' " Harris said with a laugh. "You exist in the context of all in which you live and what came before you."
The whole point is believing people aren't coconuts and that they're way more complicated than that
I agree, I just thought it worth mentioning that telling people 'don't be be a coconut' has the potential to backfire if you want them to be agreeable to whatever you say next.