If you hear that someone is speaking ill of you, instead of trying to defend yourself, you should say: “He obviously does not know me very well, since there are so many other faults he could have mentioned.”
Epictetus, Enchiridion, 2nd century
I once came across a young lad who had just started at our company. He was hired to work directly with a senior executive as a kind of personal assistant on a special project. Well, because he had the ear of the senior person, this kid seemed to instantly assume the experience and wisdom of the older guy – so much so that he irritated countless numbers of people who had been with the company longer than his five minutes. His arrogance and ignorance combination was used extensively by him to criticize anyone who came in his path. “He doesn’t know what he’s talking about, he’s an idiot.” In some cases, they were idiots of course, but rather than wait and see how the idiot performed overall, smartass ratted on everyone – fortunately the senior executive woke up finally and realized that smartass was criticising him also. Mr. Smartass didn’t last long.