Originally Posted by Bravix

Now picture this: You're sitting in the FO seat, at cruise on the last leg of the day and 5 cups of coffee in. The coffee has kept you reasonably sharp, but your bladder doesn't approve. You find yourself desperately needing to relieve yourself. After the formalities, you exit the cabin and begin heading for the lavatory when you see a 15 person long line.

You certainly can't wait in line, but you can't bring yourself to barging past 15 people who've been 'patiently' waiting.

There's only one clear course of action:

You stick your head into the cabin and let the captain know the situation...

"Ladies and gentleman, this is your captain speaking. We're going to have to go ahead and turn the seat-belt sign back on and ask you to return to your seats as there's been reports of turbulence ahead..."