wear sackcloth and ashes

wear sackcloth and ashes

To act in a way that shows one's penitence or remorse for one's misdeeds or poor behavior. Darren has been wearing sackcloth and ashes ever since his girlfriend broke up with him for cheating on her. There's no way to turn back time on the way I treated my brother growing up. All I can do now is wear sackcloth and ashes.
See also: and, ash, sackcloth, wear