Cut-throat (3-3-3)
I believe the answer is:
dog-eat-dog
(Other definitions for dog-eat-dog that I've seen before include "Ruthless competition of canine cannibals" , "Ruthless pursuit of one's own interests" , "Ruthless competition - savage self-concern" , "Ruthless competition like canine cannibalism" , "Ruthless competition as by cannibalistic canines" .)