Green’s Dictionary of Slang

mean n.

aggressiveness.

[US]R. Dennis Deadly Cotton Heart in Complete Hardman 1012: [T]hat big, black mean he carries around with him.
(con. 1961) P. Caputo Rumor of War 28: The platoon sergeant [...] Six feet three inches and two hundred and twenty pounds of pure mean.
[US]D. Woodrell Muscle for the Wing 135: Brazen dash, rough talk, and an ounce or two of mean were clearly required.
[US]F.X. Toole Rope Burns 174: He liked to see some mean in a fighter.