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.