A khaki brigade is a group of young males, usually from a private school with a dress code, who constantly roam around in khakis.
"Why's that group heading into Abercrombie?"
"Oh shit it's a khaki brigade! They're going in to raid the shitty cologne section!"
When military personnel who are usually in a lower ranking runs drills for fighting fires gets over run by the senior military personnel in charge to put out a real fire.
Petti officer: "Well, here comes the Khaki Brigade out to steal the fire we trained for."