What does the idiom 'dog in the manger' mean?

The expression 'dog in a manger' comes from a fable of the same name written by Aesop, who was possibly Ethiopian but spent much of his life in Athens. It is not known exactly when the first of Aesop's fables were written as the fables were originally handed down from one generation to the next just like a myth or a legend. It is, however, believed that Aesop lived from about 620 to 560 B.C.

Fables are short stories which illustrate a particular moral and teach a lesson to children. The theme and characters appeal to children and the stories are often humorous and entertaining. Fables can also be described as tales or yarns which have a message in their narrative such as a parable might have. Fables can often pass into our culture as myths and legends. This particular fable goes something like this:

A Dog looking out for its afternoon nap jumped into the manger of an ox and lay there cosily upon the straw. But soon the ox, returning fom its afternoon work, came up to the manger and wanted to eat some of the straw. The dog, angry at being awakened from its slumber, stood up and barked at the Ox, and whenever it came near attempted to bite it. At last the Ox had to give up the hope of getting at the straw, and went away hungry.

The expression means that people often begrudge others what they cannot enjoy themselves.