... has stirred up a distant fading memory
There is an 18 Century pub in Sandhurst (UK) that used to have a jazz session every Wednesday night - sadly no more. This was in the middle to late 1960s. A fellow trainee at work introduced my to it, and I didn't have wheels at that time so I'd go with him and a couple of other guys. This went on for a couple of years until I moved away. Another factor was that amongst my generation in the Reading areas it was, for some reason, considered 'square' (1960s uncool) to be into jazz, so I didn't advertise the fact.
There was a regular band who seemed ancient to me (so were probably in their 30s) along with guest artists. They'd play a mixture of Trad & Modern jazz, but towards the end of the evening, when we were all feeling very {ahem} relaxed, they nearly always dropped in an improvisation. Some turned out bizarre, some fantastic. Frequently they'd call to the audience for a title or theme. With hindsight I think they often had a 'plant' amongst us.
The one evening I will especially remember they had some banter as to what they should call the improv. and a mock argument. When the inevitable call to the audience came, there was an instant shout of 'Grandpa's belly's got spots'. There was considerable spraying of beer!
So the band played, I really can't remember what, but suddenly stopped and all shouted 'Grandpa's belly's got spots'. It took no time for everyone to catch on, and at every break after, the cry came back. The locals must have thought we'd all gone stark staring bonkers
