Dog in the manger

A dog in the manger is an idiomatic expression that is meant to describe a person who spitefully refuses to let someone else benefit from something for which they have no use. "We asked our neighbor for the fence posts he had left over, but, like a dog in the manger, he threw them out rather than give them to us."

The phrase comes from one of Aesop's fables about a dog lying in a manger full of hay. When an ox tries to eat some hay, the dog bites him, despite the fact that the hay is of no use to the dog.