The easiest way to pick this achievement up is to buy your way into the Main Offices area on Round 1. Once in there, look to the left of the Brew perk machine and there will be a door on the corner. If you hold
on the door you will knock and hear a man talking. Once he has finished talking hold
on the door again. Keep repeating until Samantha shouts “LEAVE HIM ALONE”.
At this point around 40 Nova 6 Crawlers will spawn in. Just melee them once each to stop them from exploding. Once you have killed of them with the knife, to mop up the remaining couple pick up an Instakill and knife them, or use Winter’s Howl or the Ray Gun.