This definition is cited by at least two books by Steven E. Ambrose, "Citizen Soldiers" and "Band of Brothers."
Soldier 2: What for?
Soldier 1: Some rear-echelon type saw me and said that I wasn't maintaing a professional appearance. I can't help it that we've been living in foxholes for the last week and because of the snipers, I can't shave.
Soldier 2: That's chickenshit.