What is the ruling on backbiting someone who has wronged you unjustly? Is gloating over brawlers by cursing and insulting them permissible, and what is its expiation? Is it considered a lie to be vague in a joke, such as making the listener believe you don't know something when you actually do?

The sin of reviling falls upon the one who initiates it, unless the second party exceeds the appropriate response. The wronged person is permitted to seek retribution in kind, without aggression or injustice towards others, such as cursing one's father, slandering, or lying. Forgiveness is better for those who are patient and pardon. There is no specific expiation for the reviler other than repentance and seeking forgiveness from the person he reviled.