cast pearls before swine
cast pearls before swine or cast one's pearls before swine {n. phr.}, {literary}
To waste good acts or valuable things on someone who won't understand or be thankful for them, just as pigs won't appreciate pearls. — Often used in negative sentences.
I won't waste good advice on John any more because he never listens to it. I won't cast pearls before swine.
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Source: A Dictionary of American Idioms