In numerous works of Halacha and Musar (ethics), the Rabbis emphasize the gravity of the sin of "Mechaneh Sheim Ra Le'chaveiro," calling a person by a derogatory nickname. The work "Orchot Chayim Le'Ha'Rosh" (Yom Shishi, 117) writes that a person who uses a derogatory nickname in reference to his fellow forfeits his share in the World to Come. Likewise, the Rambam (Rabbi Moshe Ben Maimon, Spain-Egypt, 1135-1204), in his Hilchot Teshuva (3:12), lists this sin among those transgressions on account of which habitual violators lose their share in the World to Come. The Rambam adds, however, that a violator who repents for these transgressions can regain his share in the next world, for "there is nothing that stands in the way of repentance." It should be noted that repentance for crimes committed against one's fellow includes asking that person for forgiveness.
The work "Menorat Ha'ma'or" (by Rabbi Yitzchak Abuhav, Spain-Israel, 1433-1493), in Hilchot Teshuva (chapter 3), writes that one who calls his fellow by an embarrassing name must ask that person for forgiveness and subject himself to harsh measures of atonement, including lashes and observing forty fast days. Such is the severity with which the Rabbis viewed this prohibition.
The Shulchan Aruch (Choshen Mishpat 228:5) codifies this prohibition, adding that even if the person has grown accustomed to being called the given nickname, one may not call him by that name if the intention is to insult him.
The Rosh (Rabbi Asher Ben Yechiel, Germany-Spain, 1250-1327), in his commentary to Masechet Bava Metzia (4:22), lists this transgression together with adultery and publicly humiliating one's fellow as sins for which one is denied the possibility of rising from Gehinam in the afterlife. And the Kolbo (Rabbi Aharon of Lunel, France-Spain, 1280-1330), in Siman 118, claims that a person who calls his fellow by a derogatory nickname loses his share in the next world even if he performs Teshuva. Although we may rely on the aforementioned view of the Rambam, that a violator of this sin may reclaim his portion in the World to Come through repentance, this view of the Kolbo nevertheless underscores the gravity of this transgression.
One must therefore exercise extreme care in speaking to others, to avoid saying anything that might cause him shame or embarrassment. It was customary years ago to give people insulting names based on the menial jobs they performed. This is certainly inappropriate. Nowadays, many people call one another by their last name, which in many instances expresses a lack of respect. We must ensure to show honor to our peers by addressing them and speaking to them respectfully, and to avoid using any references that may sound insulting or offensive.