* "Bite the hand that feeds you": This idiom refers to someone who treats someone else badly, even though that person is helping them. It implies a lack of appreciation for the kindness or support they receive.
* "Take someone for granted": This idiom describes the act of not appreciating someone's presence or efforts, often because you assume they will always be there for you.
* "A dog in the manger": This idiom describes someone who selfishly prevents others from enjoying something, even though they have no use for it themselves. It implies an unwillingness to share or appreciate what others have.
* "Don't know what you've got 'til it's gone": This idiom emphasizes the importance of appreciating things while you have them, as you might not realize their value until they're gone. This is a broader idiom about valuing things, but it can be applied to people as well.
The most appropriate idiom will depend on the specific context and the intended meaning.