'3. When going to the toilet/bar please wait until the end of the song – even the weakest of bladders can last out a Child Ballad – try to avoid going to the bar/toilet during the same person’s turn twice.'

Entirely fair but one night in the Southfield at Girvan an interminable song was being sung (well) about a boxing match. One guy did get up and go but on return asked "Are we still winning" as the song had still some time to its finale. Well received.
(Going twice might indeed have been frowned upon)