Our bathrooms here are single-stall affairs, and they lock. when locked, a little sign flips from "vacant" to "occupied". It's all very high-tech.
There's one woman who works somewhere on this floor, though, who can't be bothered to lock the door
so, of course, the door reads "vacant". AND that means it's unlocked, so you can just walk right in!
And then she's all indignant about being walked in on!!