Chazal said that one who calls his friend by a bad nickname has no portion in the world to come. They said further that this interdiction applies even if that person is regularly called by this nickname, and is not embarrassed by it. It follows that one who fears Hashem and is scared for his own soul, should guard his mouth and tongue from such things, and should deliberately destroy himself. If he does not know the person’s real name, or the person to whom he is speaking will not recognize the other person’s real name, he should make sure to say “the person who everyone calls such and such”. Even though by acting in this way he is free from sin, it is however, even better to rebuke the people who walk in the darkness and inform them of the severity of their actions, until they return to calling him by his real name, and by doing this he will give merit to many.
כ״ב בטבת ה׳תשפ״א
My brother and my nation, take this Torah book, in this and like this learn well, listen and revival your soul, you will achieve joy and joy, in this world and next world. (from introduction of the author) 1