It's not the waste of fuel, or the environmental impact - it's the blowing smoke in another person's face that is objectionable....
One common factor in road rage, poor driving and yes, rolling coal, is the lack of normal human social cues when both people are behind the wheel. Body language, voice inflection, facial expression...all are lacking in this encounter on the road.
I think the best approach is to ignore them...unless you have the time to follow them to their destination...at which point, you have to decide if you want a confrontation...and that choice would depend on a variety of factors, but at the very least, most State Police agencies have a hotline for reporting aggressive driving, and every cell phone has a camera for getting make, model, color and license plate.
I once followed an unbelievably aggressive road-rage driver (I watched him drive like NASCAR during morning traffic on local streets) to his destination. I had the time. But his destination was a US Navy base....and on that base, in front of his command, a whole different set of social cues came into being, and a junior sailor being addressed by a senior officer is a much different interaction than a young jerk in a pick-up truck, tailgating, cutting off, and narrowly missing, a group of anonymous drivers, including one behind the wheel of an older 4 Runner...