More on Sad Dog from Infoplease:

• Sad Dog - Sad Dog (He's a). Un triste sujet. A playful way of saying a man is a debauchee. Source: ...
• William Shakespeare: Richard II, Act V, Scene V - I have been studying how I may compare This prison where I live unto the world: And for because the world is populous And here is not a creature but m
• Dictionary of Phrase and Fable: S - Definitions, origins, and illustrative excerpts for words, phases, and literary allusions starting with "S"