I work at a Gas station.
Customer: "Hey, the bathroom door is locked. Can I get a key?"
Me: "There's no key, if it's locked there's someone in there."
Customer: "How does it know?"
Me: "How does... what... know... what?"
Customer: "How does the bathroom know someone is in there?"
Me: "People.... people go in and then they lock the door while they're using it."
[5 second pause]
This was a 20-25 year old guy, who didn't appear to be intoxicated.