To stick a fork in something means to cease whatever is happening or being said.

1) A state of completion.

2) To be completely destroyed or defeated.

1. To be done, finshed or over.
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.

Indicating a losing or lost cause, with origins in the cooking practice of sticking a fork in meat to determine when done. Also "put a fork in me," "stick a fork in you."

To be done, done with it.

Exhausted, used up, finished. From meat that is fully cooked and ready to be handled with a fork.

Meaning that something is definitively finished such that whatever it is doing (or being done to it) should or can be stopped, or considered to be done.

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.