You'll get this while working toward the "Heavyweight" achievement,
If you complete the game without getting this achievement, you should load up "Escape The Embassy" level, kill the first 3 guards without using takedowns, then reload, rinse and repeat.
What button combo you use is up to you, it doesn't make any difference, just do not kill them using takedowns
I've linked in a video so you can see the section I'm on about, it's literally just the very start of the video. You'll see him beat up the guards, ignore the method he uses and just make a note of the 3 guards you should be killing over and over.
*Credit to StumpedGamerPreview for the video