Dog in the manger (UK) If someone acts like a dog in the manger, they don't want other people to have or enjoy things that are useless to them.So the person is refusing to share something with others.
The original dog in the manger was a character in a fable - a dog who insisted on sleeping in a manger and not letting the animals eat from it (see the full story here: The Dog in the Manger - Wikipedia, the free encyclopedia ). The usual expression is just 'Don't be [such] a dog in the manger' - adding the adjective suffix strikes me as a bit odd. Maybe it's characteristic of some other dialect than mine.