The noble and polite character of Rasulullah (Sallallahu Alayhi Wasallam)

I read somewhere that the Holy Prophet sallallahu alaihi wasallam at some occasions used harsh words to people. It was written that he would impugn then. Is the definition of impugn which is meant in the ahadith ‘to cause people to doubt someone's character, qualities, or reputation by criticizing them’. Also when we say harsh words, what was the manner of the Holy Prophet sallallahu alaihi wasallam in that case? Did he say the words in an angry tone?