When events such as SFO occur, PPrune is full of people complaining that PAX ignore safety instructions. But they are TOLD to ignore safety briefings.
Here is a current Easyjet safety briefing.
IMG_0571 | Flickr - Photo Sharing!
There is a drawing showing how to adopt the 'brace' position, but everyone on board, from the captain down, must know that it is IMPOSSIBLE to adopt anything like this position in any of the seats on the aircraft.
IMG_0574 | Flickr - Photo Sharing!
The only assumption that any intelligent passenger can make is that these instructions are a pure meaningless formality, and that neither the captain, nor the flight crew, nor anyone in Easyjet management expect passengers to take any of this information seriously.