Does insulting a person or behaving improperly toward them while fasting invalidate the fast?

Sins like cursing and swearing do not invalidate the fast, but they diminish its reward and may even nullify it. Fasting is not merely abstaining from food and drink; it is also abstaining from disobeying Allah to achieve piety. Allah Almighty said: "so that you may become righteous." The Prophet, peace and blessings be upon him, said: "Whoever does not give up false speech and ignorant deeds and acting upon them, Allah has no need of his giving up his food and drink." The fasting person is commanded to guard his limbs, so if someone curses him, he should say: "Indeed, I am fasting."