I'm sure everyone knows that one cannot "lock" themselves in an airplane rest room.
If you haven't seen the flight attendants prepare the planes for takeoff and landing, there is an outside latch that locks/unlocks the doors. The small metallic sign that says "Lavatory" on the door is hinged at the top. If you flip up that sign, you can slide the same latch that you do on the inside to lock/unlock the door.
If you ever need to get access to the inside in a hurry, that's how to do it.
-PJ
Your information may prove to be of tremendous value since we are no longer going to be allowed to use the lav if the flight is less than 90 minutes long.Look for longer clean ups of the planes and wet cushions.