This
database is a comprehensive collection of all the American idioms and slang available.
American Idioms are many and varied. We hope you enjoy our collection. We are adding more all the time.
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(UK) People, especially couples, who argue in front of others or involve others in their personal problems and crises, are said to be washing their dirty laundry in public; making public things that are best left private. (In American English, 'don't air your dirty laundry in public' is used.)
you cannot change someone's basic human nature or bad qualities
The manager wrote a letter of apology to the customer but a leopard can't change its spots and I do not believe that the manager has changed and the letter does not mean anything.