You think shooting unpopular officers in the back started in Vietnam.The root of it is from the term 'Fragging' from the US military in Vietnam, meaning to kill or assassinate an unpopular or incompetent officer. This was often achieved using a fragmentation grenade for plausible denyability (the enemy threw it, i threw it but it fell short, etc).
This then morphed into the term 'frag' for FPS games in the 90s. Meaning to kill someone.
See http://en.wikipedia.org/wiki/Fragging
That. . . is. . . just. . . so. . . damn. . . CUTE!