from a misreading of "to kill a mockingbird" when they poke under the bed with a broom handle. a grunt under the bed.
B. huh uh. you just had one.
A. yeah, i know. i didnt want to say, i'm actually going to do a grunt.
oooh, did you see that nasty grunt in the shitter? it didnt flush!
The term GRUNT also refers to those doing their time commitments and getting out during the Vietnam War; as opposed to Lifers who were career Marines.
The term POG is the opposite meaning "Personnel Other than Grunt"
Marine GRUNT: Stay out of our way before you catch one between the eyes ya damn Hoo-Ah
If John Wayne was a Marine he'd be a fuckin' GRUNT.
POG: Damn I have so much paper work to do
GRUNT: Stop bitchin' you fuckin' POG