Well explained, JohnB ! I played it in Birmingham, but it may well be from further north: most of the others were from Yorkshire (but *not* 9Hull9).
"Sacred Dido" is a trying-desperately-to-keep-a-straight-face game. One person is the "Most Honoured and Beautiful President" and must always be addressed as such. All kinds of bowing and acts of reverence can be added to the routine, as directed by the Honoured President. The others sit cross-legged, backs and faces straight, and are named 'Brother 1', 'Sister 1', 'Brother 2' etc. The court sits in silence. If anyone sees any of their fellow brothers or sisters not abiding by the rules of Silence, Stillness and Solemnity they complain to the President and punishments/forfeits are suggested and given out. As the game goes on, it becomes a competition of landing your mates in it more than they have to you.
This game was originally intended to train actors not to "corpse" - and, believe me, it is just plain hilarious. As JohnB says about FizzBuzz - you have to be there, really, to understand it. Or not.