I agree that this points to deeply rooted a deeply rooted mindset and behavioral issues. At the same time though, this is an opportunity to do the right thing and attempt to show the guy that this is a fundamental and not compartmentalized problem he has (not that I'm criticizing the entrepreneur here).

Maybe, over time, this will resonate with him, when he sees other people's reactions when this happens again. If not, you've done all you could.

If the investor hasn't learned these things before now, there are good reasons to suspect he won't change overnight. Even if he thinks it over, he may do a cost-benefit analysis and come to the conclusion that for him, personally, it works out better to shout at the waitress. Possibly because the coffee really is that important to him. Possibly because it weeds out business partners who don't like his style.