Dog in the manger is an idiom for a person who keeps others from having or using something, even though that person has no use for it. The idea is selfish obstruction, not simple ownership.
The expression comes from an old fable. A dog lies in a manger, which is a feeding trough or rack holding hay for horses or cattle. The dog cannot eat the hay, but it snarls and stops the animals from eating it. That image led to the modern meaning: blocking others from something you do not even want for yourself.
This idiom is often used when someone refuses to share, delays access, or prevents progress for no good reason.
- She never uses the garden plot, but she will not let anyone else plant there. That is a dog in the manger attitude.
- He did not want the project lead role, yet he objected whenever someone else was suggested.
People usually use the phrase critically. It suggests pettiness or spite, not fairness. If someone is simply protecting their own property for a clear reason, this idiom may be too harsh. Use it when the real problem is stopping others for the sake of stopping them.