Tim Bowen discusses the unusual idiom a dog in the manger.
Overheard on a tube train in London, a building labourer addressing a smart city gent: “Excuse me. Are you reading that paper you’re sitting on?” Interpreted literally, the question is ludicrous, unless the person sitting on the newspaper has an ability to read through their backside, but the intended meaning is clear (the questioner wants to borrow the newspaper and is politely enquiring whether the other person has finished with it). An unfortunate choice of words perhaps, but clear nonetheless. The monosyllabic answer, however, was quite unexpected but equally clear: “Yes”. In other words, “I don’t want to let you borrow my newspaper even though I am clearly not reading it at the moment”.
This is a classic case of a dog in the manger, someone who does not want or need something but will not let other people have it. A manger is a long, low open container with hay in it for horses, cows and other animals to feed on. The expression is said to originate in the tale of a dog that habitually slept on the hay in a manger and growled at the other animals when they came to feed on the hay, although the dog, not being a vegetarian, did not want to eat the hay itself. Young children are probably the best examples of dogs in the manger, refusing to let other children play with their toys even though they are not playing with them themselves. The expression does not only apply to children, however, as the example in the tube train clearly shows.