Green’s Dictionary of Slang

(US black) violent, thuggish.

1928		Blind Lemon Jefferson ‘Prison Cell Blues’ [lyics] Got a red-eyed captain and a squabblin’ boss / Got a mad-dog sergeant, honey, and he won’t knock off.
1948		H. McCoy Kiss Tomorrow Goodbye in Four Novels (1983) 105: Toko had suddenly blossomed into a vicious criminal, a mad-dog killer.
1966		H.S. Thompson Hell’s Angels (1967) 47: The Frisco Angels refused, but they were badly unnerved by the mad-dog raids from Oakland.
1991		L. Bing Do or Die (1992) 81: He looked at me crazy, give me a real mad-dog look.
1997		E. Little Another Day in Paradise 21: Whoa, tough guy [...] Before you go into your mad-dog routine, you should make sure it’s warranted.
2015		J. Stahl OG Dad 203: She’s eyeballing me, giving me the pre-crawler mad-dog treatment.