You’ll probably want to aim for this achievement in the Crash Site gametype, but TDM will also work well. You’ll want to start out with your least favourable weapon, and work your way to the better one. When you spawn, try using your grenades in a crowded area to score a kill, and remember to cook them to easily kill camping enemies. Now try to sneak up on someone using cloak with your secondary weapon preferably from behind, and then score a kill with your primary weapon. There’s not much else to say here, just go out and try your luck.