Military. A very unpleasant thing. So named from squadie wanking contests. The resulting 'barrack room biscuit' is covered in a lot of spoodge (and is usually force fed to the last man to shoot).
Dude 1: "D'ya see that chick's face in 'Bukkake Cum-fest Volume 9'? What a mess!"
Dude 2: "Yeah, Dawg. Bad as a barrack room biscuit."