Rear facing seats
Back in 1999 (I think) I flew from Palma to Stansted on a British World BAC
1-11 and had the misfortune to be allocated a rear facing seat. It was directly opposite the people facing forwards, either side of the central emergency exit, so that we were fighting for the space on the floor for our feet. Very uncomfortable, but fortunately only a short flight.
I can't remember if there was a forward facing safety demo for the backward facing passengers but I do remember that no mention was made of adopting a different brace position. As far as I could see we would have smashed our heads against each other in the event of an accident.