Well, hope I don't get too slammed for this...
but I gotta wonder what his concern was.
It is environmentally unmindful to just let a vehicle run for no reason, gas or diesel.
If he was in a situation where the fumes were making him sick or he couldn't get away from the noise...
You did say, in a rather uncompassionate way, that he was in an unhealthy state.
Maybe he has a health problem which fumes exacerbates.

Conventional wisdom says that he should have just gone elsewhere, and he sure could have said it nicer, but some folks take it upon themselves to be an enforcer. If he really wanted to be a jerk, you would not have heard from him at all. You would have found yourself face to face with a cop.
I too have been annoyed in the past by thoughtless folks who pollute with no concern to people around them, usually it is people throwing garbage out their windows. I can't stand that. And as a motorcyclist, I got real reasons why that is more than just an inconvienence; it is a road hazard.

BTW, it is not legal where I live to idle long, or idle at all at a diesel pump.
There are valid reasons for this.
Seems to me that people need to be a little more understanding in this world, and in this case I think both parties failed....

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Think Alternative Energy!
300CD '80 (now gone but not forgotten...)