Now as the earliest place to get this is as part of the story, spoilers shall be warned of!
*** Spoiler - click to reveal *** During the quest 'The crocodiles Jaws' (LVL 28) you will be tasked with entering the arena at Krokodilopolis. After three random fights against mooks you will be task with fighting the gallic brothers.
During the fight with them let your adrenaline build, and save it until one of the brothers is near death. Use & to finish him off. It doesn't matter which brother, and it doesn't have to be the one that ends the fight.
If you don't do it at this point then when the arena is open proper (after killing the crocodile) you can fight any of the boss battles, and finish them off with a well timed
&
overpower. The moment their health reaches zero because of the attack, the achievement should pop.
You can obviously do this whilst also trying to get
Let's keep cheevin' together!
EDIT: I have had numerous comments of this not popping for people. I think this achievement might bug out for a few people and for that I apologize but as of yet have no solution.