On the day of this update (07 Dec 2017) you can get the achievement in coop vs AI game on casual, I have done it right now. Be quick in case they change it.
In order to get the achievement you have to do at least 10 kills without dying in the match. So be sure to choose a game mode in which you can do at least 10 kills, I recommend King of the Hill.
EDIT: Still works on Jan 13, 2023 (Thanks Blckbird007).