Does one who says, "You have expelled me from my madhhab" or "You have made me a kafir" apostatize from the religion, and must he seek forgiveness and perform ghusl? And does insulting the religion in a moment of anger fall under disbelief and necessitate repentance and ghusl?

Seeking forgiveness presents no problem. However, ritual bathing is problematic if it indicates a judgment of disbelief (kufr). The phrase "أخرجتني عن مذهبي" (you expelled me from my madhhab/school of thought) does not necessarily imply the religion of Islam. As for the word "كفرنتني" (kaffarantani), if it is intended to mean "كفرتني" (kaffartani), in the sense of "you made me disbelieve," then this word carries difficulty and constriction. Anyone who utters a word of disbelief in jest or playfulness has disbelieved, according to all (scholars). One also disbelieves by saying "Labbayk" (at your service) or "We are likewise" in response to someone who says, "O disbeliever," or "O Magian," or "O Jew," or "O Christian." And whoever utters a statement that expels him from Islam, such as saying, "He is a Jew or a Christian or a Magian," is a disbeliever. Therefore, one must avoid these terms to safeguard the religion. However, if the prohibited meaning is not intended, and it is merely meant to express anger, then there is no problem with it.