Amusement park (or theme park) parking lot lingo to describe the horrific realization that you've forgotten where you parked your car. Originates from the Simpsons episode where they go to Itchy & Scratchy Land, 'The Violentest Place On Earth', where Homer says "Remember... we parked in the Itchy Lot", and the camera pulls back to reveal that there are only two lots, the Itchy Lot and the Scratchy Lot, each filled with 50,000 cars.
...walking out of Giants Stadium after the Metallica concert...
"Hey that was a great show! Uh-oh, where did we park?"
"I think we're in the Itchy Lot"