The way I see it this guy knew that his job would involve close contact with unhappy people on a daily basis when he started it.

If he can’t do it professionally perhaps he should find something less difficult on his fragile ego.
I don’t care how his day is going.
If he pulls me over he needs a good and correct reason and needs to understand that neither his uniform
nor his “Having a bad day” gives him license to be a prick.