The Ben Ish Hai (Rabbi Yosef Haim of Baghdad, 1833-1909), in Parashat Ki-Tese (12), discusses a number of prohibitions regarding the way one speaks to others. First, he addresses the prohibition of "Genebat Da’at" (literally, "stealing one’s mind"), or misleading another person. The Torah forbids misleading another person even if the misleading information will not cause a financial loss, but will leave the other person feeling indebted. The Ben Ish Hai gives the example of an extending an invitation to one’s fellow knowing full well that he has already made plans to eat somewhere else. If a person knows that his friend is eating Friday night dinner with his parents, for example, it would be forbidden to extend to him an invitation so that he would feel a debt of gratitude. Similarly, the Ben Ish Hai writes, if a person knows that his friend is observing a fast, such as on Ereb Rosh Hodesh, he may not offer him food or a drink, misleading the person into thinking that he is sincerely making a genersou offer.
The Ben Ish Hai adds, however, that this prohibition applies only if one extends the invitation in a persistent manner. Simply stating one’s desire that his fellow join him for a meal is often done as a common, salutary greeting, much like saying, "Good morning" or "How are you." People will often say, "Why don’t you come by?" as a friendly greeting, and not necessarily as a sincere invitation. The Ben Ish Hai writes that one may extend a perfunctory invitation such as this even if he knows that the other person cannot join him, since the "invitation" is stated simply as a friendly greeting. The prohibition of "Genebat Da’at" applies only if one asks persistently that the other person join him, knowing full well that he had already made other plans.
The other prohibition addressed by the Ben Ish Hai in this context is that of "Ona’at Debarim," or verbal abuse. He writes that just as the Torah forbids "Ona’at Mamon," cheating other people by overcharging for merchandise, it similarly forbids causing a person pain through words. In fact, he adds, causing a person harm with words is a more grievous sin than overcharging, since the latter can be rectified by returning the money. Words, however, cannot be retrieved once they are spoken, and the harm they cause cannot be undone. Moreover, causing harm through words hurts a person directly, as opposed to "Ona'at Mamom," which affects only his finances. For this reason, insulting one’s fellow is considered a more severe Torah violation than cheating him financially.
The Ben Ish Hai notes that "Ona’at Debarim" is not confined to berating and shouting explicit insults at one’s fellow. It includes any speech that causes one’s fellow distress, including calling him by a nickname to embarrass him. The Ben Ish Hai emphasizes that even if a person has grown accustomed to a certain nickname and is no longer ashamed by it, one who calls him by that name for the purpose of embarrassing him transgresses the Torah prohibition of "Ona’at Debarim."
Summary: It is forbidden to mislead another person, even if there is no financial loss entailed. For example, if a person knows that his friend had already made plans for lunch, he may not persistently request that he join him for lunch, since this request is insincere. It is, however, permissible to extend a brief invitation as a courtesy or as part of a friendly greeting. It is strictly forbidden to say something insulting to one’s fellow, and this is a more grievous sin than cheating one’s fellow financially.
