v. "Stick a fork in me"
In reference to a piece of meat or sausage, whereby one sticks a fork in it to test if it is properly cooked.
From grilling -- not to test whether something is done, b/c that wouldn't make any sense, given what the phrase means. Instead, to stick a fork in the piece of sufficiently-grilled-meat so as to take it off the grill. Connotations of definitive doneness enhanced by sub-conscious notion that the piece of meat is not only completely cooked, it is no longer reasonably conceived of as part of a living animal, and thus can be stabbed with impunity.