I recall once as we were rolling down a particularly bumpy taxiway after landing, a lady ran up the aisle to the loo that was beside my crewseat. I gave her the requisite "Madam, you must return to your seat until we have reached the gate ..." but she said she
really had to go. What to do, right? So I told her to make it quick and to take care steadying herself in there. As soon as she was done and had opened the door, I told her, "Now quickly, sit down please!"
"Okay," she said agreeably ... then promptly went back inside the loo, shutting the door!
I was dumbfounded, as were the passengers sitting around the area. As she did not lock the toilet door, I stood up, pushed it open, and found her, fully dressed of course, sitting very obediently on the closed toilet seat, hands folded on her lap.
I tried very hard to keep a straight face as I gently clarified my request. Don't think I succeeded, though!
