One of the most over used and lamest of all sayings. Bears little meaning anymore. In the same outdated category as terms "dont go there" and "talk to the hand"
A US Air Force cargo plane fully loaded with combat equipped US Army Paratroopers - Some of the nations most unequivocally certified bad ass motherfuckers - on their way to a real world, or simulated airborne insertion.
When those Paratroop Doors open over what ever third world shit-pile they've been dispensed to, and that jump caution light turns green all manners of whoop-ass will assuredly commence on the ground below.
see LGOPS
You see that C17 Globemaster out there on the tarmac son? That Aircraft can hold 102 combat equipped paratroopers. When the President picks up the red phone and dials, they can have that can of whoop ass in the air smokin, headed anywhere in the World in 18 hours or less.
the term has been popularised, among other things, by one of the mightiest and most well-known gaming clans that participate in the famous FPS on-lnine game Far Cry: {TAF} (The Animal Farm).
As everyone in the Far Cry community knows, "For those times a can of whoop ass just isn't big enough: {TAF} In A Can!"