Is it permissible to mock someone who mocked me, or to belittle someone who belittled me, in kind?

It is not permissible to mock or belittle a Muslim, based on Allah's words: "O you who have believed, let not a people ridicule [another] people; perhaps they may be better than them" (Quran 49:11), and the Prophet's (PBUH) saying: "A Muslim is the brother of a Muslim. He neither wrongs him nor abandons him nor despises him."

However, if a person is wronged or aggressed against, it is permissible for them to respond in kind without exceeding the bounds, based on Allah's words: "And the retribution for an evil act is an evil one like it" (Quran 42:40), and "Allah does not like the public mention of evil except by one who has been wronged" (Quran 4:148). This includes supplicating against the oppressor or exposing their injustice without lying or transgressing, although forgiveness remains superior.