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 it."
“Let me explain, you're 25 now and will likely stay pretty hot for the next 5 years, but less so each year. Then the fade begins in earnest. By 35 stick a fork in you!”
by sensitivitytothings May 4, 2008