Good for him.
I've shouted "puerco" at drivers who've thrown stuff out of car windows and said "se le cay? algo" to people who've dropped litter on the street.
I once asked a taxi driver if he loved his country; of course he said yes, so then I asked him why he'd thrown a styrofoam cup out of the window.
My son once made Mr C. stop the car and made his friend get out and pick up the bottle he'd chucked out of the window.
Once, by the river, I went over to the other group that was picnicking there, said hi and chatted for a few moments telling them how as a foreigner, how impressed I was by the beauty of the place and how important it was to look after it.
They agreed wholeheartedly, and I gave them a couple of plastic bags, "para recoger la basura", thus preempting any situation, and it did actually work.