What is the ruling on using the terms "infidels" (kuffarah) or "son of a whore" (ibn al-'ahirah) in insults and curses, given that their use in Egypt may not be intended to convey the original, literal, Shar'i meaning of the words?

It is not permissible for a Muslim to say to another Muslim, "O disbeliever," due to the severe warning mentioned concerning this. Nor is it permissible to insult with the phrase "son of a whore," because it is an accusation of unchastity, and unchastity means fornication. Saying "O son of a whore" is like saying "O son of an adulteress," which is an accusation against the mother. If the mother is deceased, the accusation is against the son. The fact that people use it for the purpose of insult does not change its ruling as an accusation, and this differs from the change in custom regarding the use of some words.