This is a viral achievement gained in multiplayer by killing a player that already has it.
The prevalence of this achievement is very high (over 90% of TA players who have started this title update have it *Edit* this was the percentage before TA included TUs as part of the main game. Even now, it's still around 80%) and you will very likely get this in the first game you play, in fact I got it on my very first kill.
To increase your chance of getting kills, I recommend team play and 'stealing' someone else's kill. Try and get the head shot on an opponent with downed shields. Other ways to get easy kills are to use vehicles or camp by a doorway and melee an unsuspecting enemy in the back when he runs through.
This achievement will definitely come with time. Good luck!