Navy slang (specifically used by SEALs) to refer to an exercise (
aka "evolution") whereby the trainee combines vigorous exercise on the beach with
cold surf, alternating between running back and forth between the waves and dry sand, building up a coating of sand against the trainee's shivering
skin, much like the superficial crust of sugar on a delicious sugar cookie.
Used more generally to indicate the trainee is about to suffer from
cold and exhaustion.