Green’s Dictionary of Slang

(orig. US) to subdue physically, to kill.

1833		D. Crockett Sketches and Eccentricities 145: I can kill more lickur [...] and cool out more men than any man you can find in all Kentucky.
1960, 1975		Wentworth & Flexner DAS.
1972		D. Jenkins Semi-Tough 101: If a One danced, she could cool out everybody else on the floor.