An expression used to convey the utter hopelessness of a situation, given that everything has gone wrong with little or no chance of salvaging.
Biff: "Hey, Melvin - you know how you and your twin brother have been swapping girlfriends every other week?"
Melvin: "Hellz yeah...pretty sweet, huh?"
Biff: "Not really...someone spilled the beans, and now your girlfriends know."
Melvin: "OH NOES!! The s*** has hit the fan!!"