Not a FAA requirement.
Guess you missed my satire.I'm well aware that it is not an FAA requirement, and quite frankly, I've never seen one of the curtains. However, it sounds like a great idea to me. I still have passengers come up the aisle and attempt to move the cart so that they can go to the F/C lav. They get highly incensed when I tell them they have to go to the back or wait at their seat until the cart is removed.
Even when I try to explain that one of the cockpit members is using the lav, their response is "So?"