put on, wear, etc. sackcloth and ashes

put on sackcloth and ashes

To act in a way that's intended to show one's penitence or remorse for one's misdeeds or poor behavior. Darren has been putting on 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 put on sackcloth and ashes.
See also: and, ash, on, put, sackcloth
Farlex Dictionary of Idioms.

put on, wear, etc. ˌsackcloth and ˈashes

behave in a way that shows that you are sorry for something that you have done: Look, I’ve said I’m sorry! What do you want me to do — put on sackcloth and ashes?This comes from the Bible. People wore sackcloth (= a rough material) and put ash (= the grey powder left after something burns) on their face and hair to show that a person they loved had died or that they were sorry for something they had done.
See also: and, ash, put, sackcloth
Farlex Partner Idioms Dictionary
See also:
  • be in (one's) good graces
  • be in somebody's good graces
  • be in someone's good graces
  • at doorstep
  • at (one's) doorstep
  • at (one's) expense
  • at expense
  • at somebody's expense
  • at someone's expense
  • be remembered as/for something