Once upon a time, there was a Monday night contra dance in the center of Amherst. Its history is another story, but one of its salient features was a sit-in band–cheerful, friendly, engaging, fun, and a fine way for musicians to play out. Then it was decreed by the new organizers that there would be no more sitting in, so what were the musicians to do? Sit home and sulk? Of course not. So began the Monday night session, not in Amherst, but a few miles north in the village of Montague Center.
See David’s comment below for a more detailed version and a few conversational gambits.