I always find this "implacable enemies" stuff risible.
It's meant to be a sort of compliment, but always seems to be a way to describe violent, unorganised atavistic simpletons, who are fine if you leave them alone and then react like enraged chimps when provoked.
It's a bit like those fucking halfwitted cunts on social media who describe themselves as "slow to anger" and "the best friend you could ever have, but also the worst enemy you will ever make", like their vaguely autistic, social awkwardness is in any way impressive, laudable or even vaguely interesting, and making an enemy out of someone who works part-time at Timpsons would be a genuine ongoing problem.