Prior to starting pilot training (some time in the dim and distant past), I clocked up a few squillion hours as SLF. I was one of the guilty ones who plonk posterior in seat and get on with reading the Times.
Then one day I was joined by a senior widebody (dont remember the type) P1 who was deadheading. He was a fountain of knowledge and very amiable, but his take on the safety brief was best:
"you may know the safety brief, and so may I, but just think how disheartening it must be for the cabin crew to stand there and see people's heads and not a single pair of eyes".
Good point! I now always pay attention out of courtesy to the cabin crew.