It is permissible to speak negatively about someone who was guilty of verbal abuse, in order to comfort his victim. The pain and humiliation caused by insulting speech can be minimized by pointing out to the victim that the perpetrator lacks intelligence or discretion and that people do not take him seriously.

At a later point in time, it would be important to help the victim understand the nature and problems of the perpetrator so that he can learn how to deal with the person and prevent recurrence of such incidents.

Sefer Cofetz Chaim, 9 Kislev, Page 186

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