You might hear this expression from time to time: “Stick a fork in it.”
As with most expressions you aren’t supposed to actually spear anything with a fork. The expression indicates that something or somebody is done, finished, over with.
For people a situation might be like this: you have just been cross country skiing for 30 miles and your skiing buddy asks you: “you want to go another round?” unless you are in Olympic condition your answer could be: “stick a fork in me. I am done!”
An example for sticking a fork into a thing is this headline: “Stick a fork in it. Pass the Child Nutrition Act.”
Since this expression does not have its origin in sports it must be food. And so it is: when cooking meats or sausages one often sticks a fork in it to see whether it is done.