Nickname for one who is short in stature and tends to overcompensate for it - often through short temper, learning martial arts or other fighting skills, or attempting excessively difficult tasks. This is of course referring to Napoleon Bonaparte's conquest of Europe; Napoleon himself was very short, and there is an old inside joke among historians that his drive to conquer came from his lack of height.
Short dude: What are you lookin at? You wanna start something?
Tall dude: Whoa, Bonaparte, mellow out.