a dog in the manger 占着茅坑不拉屎的人
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.