I was once on a Lufthansa flight over the Alps. We hit some 'severe' unexpected turbulence and the aircraft was taking a bit of a shaking. Some of the passengers were screaming and clearly very frightened. The wings were flexing, as of course they are meant to. The captain reassured everyone over the PA that the flexing of the wings, and the stresses, were a fraction of what it was designed to take, and that there was nothing to worry about. Of course the rest of the flight was uneventful and we landed safely.
The captain was standing by the cockpit door and nearly every passenger who disembarked thanked him.