It's helpful when a restroom has a little "vacant/occupied" slider that goes with locking the door, maybe in a stylish two-color red & green thing. Helps you know how to approach the situation.
For me, when a bathroom tells you it's occupied, I can't help, I CANNOT HELP but think of the word occupied as "kaka-pied", as in a pie of kaka is being applied to it.
Occupied? Occupied with what? Occupied with kaka! Specifically, a pieful of it!