Politeness is free.

What would happen in a bar if you treat the barmaid like that?

'Hey stupid where did you learn to pour a beer like that?'

Or a police officer (your taxes pay for his job).

'Did you ever learn how to use a radar gun or a alcohol tester? The way you use it is stupid.'

That attitude will not get you far in life. Be polite, particularly with someone you are angry with and play the ball not the man.