Us/west (hp) Fleet

i think it came from the British Airways wetlease
That is correct! Lord King and Sir Colin Marshall required all crewmembers in Full Dress at all times.....even sporting the derby hat that was issued. With the Royal family as large as it is, by having F/A's stand at attention at all the bulkheads The Peasants would be readily available to GREET the Royals....to bow/curtsey/salute or do a backflip. And now YOU know why we terminated the alliance :p (As you can see I am having a little fun with this but, THE STANCE did originate from the Wetlease.......flying "The World's Favourite"
 
The only thing good about standing in the bulkheads for the demo is to give the finger behind your back to your fellow f/a behind you trying to make them laugh. One girl I would fly with all the time would pick her rear end and all kinds of crazy stuff to get me laughing. Trying to hold your laugh only makes is worse. Of course the passengers are looking at you like your crazy and that adds to it as well.