Hey,
I cannot remember ever being locked in a bathroom, but a couple of times I have had the lights turned off on me while I was inside.
The bathroom in my office building has no windows and without lights is "blacker than the inside of a cow"!
I need my keys to get back into my work area of the office so I always have them with me when I go to the bathroom, and on my keys is my EDC mini-LED, problem solved.
Mike