What is the ruling on saying "You have ruined the the religion of the Umm (Islamic nation) today" to someone in a state of anger? Is this considered reviling the religion, and what is the expiation for the one who says it?

This phrase is not disbelief (kufr) nor an insult to religion, and there is no expiation for it unless the speaker intended to insult the religion of Allah the Almighty. Days do not have a religion, and whoever says "you ruined my religion for me" is not considered to be insulting unless they intended to insult, as reported from Ibn Abbas. Nevertheless, a Muslim should avoid such phrases so that Satan does not lure them into insulting religion, and they should guard their tongue except for good, in accordance with the Prophet Muhammad's (peace be upon him) saying to Mu'adh ibn Jabal: "And will people be thrown into the Fire upon their faces except for the harvest of their tongues?"