I was in a single toilet restroom in the mall once, and this person came and tried to open the door. It wouldn't open, so they tried it again. I figured, okay, now they'll get the clue and cut it out.
Nope. They yelled to someone, "the door is stuck and won't open," so I finally said, "there's someone in here!" They responded, "Oh," and were not out there when I got out.
I just don't understand doing that. It's like they never encountered a locked door before.