FNG    - I am not sure of the origin, but I was the first person in my unit to use the term "FNG",  (F___ing New Guy) to refer to the new replacements.  We normally teamed them up with an old timer who would try to keep them alive long enough for them to learn the ropes.  They were KIA more often than any other group.  Their lack of experience and fear were often fatal. This explains why we were reluctant to learn their names at first.  They were usually referred to by job title or FNG or a nickname. The less you knew about them, the less it hurt when you had to zip them into a body bag.