wear sackcloth and ashes
From Longman Dictionary of Contemporary Englishwear sackcloth and asheswear sackcloth and ashesBritish EnglishSORRY/APOLOGIZE to behave in a way that shows everyone you are sorry about something wrong you have done → sackclothExamples from the Corpuswear sackcloth and ashes• I have no wish to see Aitken go through the rest of his life wearing sackcloth and ashes.