Green’s Dictionary of Slang

(US black) competitive, ruthless, lacking in compassion.

1993		Snoop Doggy Dogg [song title] It’s a doggy dog world.
2000		P. Beatty Tuff 47: ‘One hundred moneymaking entities run by punctual niggers who’ve achieved something in this doggy-dog world.’ ‘Dog-eat-dog,’ Yolanda corrected.