Don't assume all delivery drivers get paid minimum wage. I delivered pizzas for a year and wasn't paid minimum wage for the hours I was on the road, which was usually the majority of my hours. I was given $1 bybthe restaurant for every delivery I did, but that's hardly enough without a tip unless I took out a large volume of orders without driving far. When you factor in how much gas it takes (a long shift might use most of a gas tank) and how much wear and tear a car doing delivery takes, minimum wage doesn't begin to cover it. Not to mention if you deliver to any rough neighborhoods, there's a risk of being a victim of crime. A driver that worked at my restaurant was shot the year before I worked there. I quit after someone attempted to mug me with a stun gun at 2am, less than a mile from the restaurant.

I do agree that you should never argue with a customer over tips. It's unprofessional at best. Save the bitching for your coworkers when you get back to the restaurant. And the comment about OP's race is wayyy over the line. That makes the driver the primary asshole in this situation. It's a good thing you reported him, because he should be fired for that.

My vote is (just barely) ESH. OP, you are barely an asshole in this situation, but in the future, please tip delivery drivers. If my experience was at all normal for most drivers, there's a good chance they're struggling for money, and every little bit helps. Even if it's just a dollar or 2, any drivers serving you in the future would greatly appreciate it.