Where Did It Come From?
The Dog In The Manger is an ancient Greek fable which is frequently ascribed to Aesop (620-564), but actually predates him by some time. Essentially, the fable tells of a dog which was lying in a manger; he of course did not want to eat the grain in it himself, and yet he fiercely growled and wouldn't let the ox (or horse, depending on the version) eat it either.
The Dog In The Manger got tangled up with Aesop around 1480 when a German printer named Heinrich Steinhowel published a version of Aesop's Fables and decided to toss in the fable to illustrate a moral principle:
So that's where the expression "dog in the manger" comes from... hopefully we regard this fable in the light it was offered: as a condemnation of behaving in a stingy, spiteful, and mean-spirited way towards others for no reason other than perverse personal satisfaction.