It's not actually that hard:

A) They politely provide reasons, citations or rational for their opinion and may ask you to address those concerns.

B) If their time is too valuable and mine isn't there had better be a significant actual differential in our importance in the world. I'd take it from my CEO, but I expect explanations from anyone under him. Otherwise the "brusque" answer is like someone who doesn't bother capitalizing and using proper punctuation: a mark of disrespect for my time.

C) The nice guy having a shitty day feels bad when you call him on acting like an asshole.