出自《伊索寓言》（Aesop's Fables），有一篇狗站马槽的故事，说的是一头狗躺在堆满稻草的马槽里，狗是不吃草的动物，而当马或牛一走进稻草时，这头狗却朝着马，牛狂哮，不准食草动物享用。因此，“狗站马槽”就成了一个家喻户晓的成语而进入英语中，常用来比喻a person who prevents others from enjoying sth that is useless to himself； a churlish fellow who will neither use a thing himself nor let others use it，讽刺那些占据说职位或某些物质却不做事的人。

    a dog in the manger是个名词性短语，常与系动词连用，充当表语（主语补足语）

    eg：He borrowed a lot of books from the library，but he didn't read a book.He was really a dog in the manger.

    There are some officials who are only the dogs in the manger.

    Smith was a dog in the manger over that roll of wire；it was no use whatever to him，but he wouldn't let us have it.