In essence, a baby wipe bath. Named after the style in which soldiers (more specifically, US Army Rangers) perform personal hygiene while deployed or in the field, or any other time a bath/shower is not available.
I didn't have time to shower before my date, but I did Ranger Douche.
A player that chooses to use dual Rangers(shotgun) in Modern Warfare 2, spending their time running around corners and completely blowing them away. Most Ranger Douches like to add insult to injury, spouting obscenities through a bluetooth device.
Denzel1293: Fucking shotguns, man.
Halleberrie: l o l, you totally suck
Denzel1293: I just got Ranger Douche'd.