The mustache grown by a male soldier during a deployment. Commonly characterised by its tendancy to make the wearer of said stache look like a child molester, and/or a 1980's action actor. Also the combat stache has a tendancy to be outrageously out of reg.
PVT: Dude Sgt Snuffy's wife would have a heart attack if she saw that ridiculous mustache on him!
PV2: Ya he's gonna shave it before R+R, its just a combat stache.