I try not to sing in sessions these days for that very reason. However I remember singing As I Roved Out (the 'married the lassie that had the land' one, not 17 Come Sunday) and found this pillock trying to accompany me on a soprano sax. It happens that said tune is very flexible and lends itself to endless rhythmic and melodic variations, to say nothing of changes of tempo. He gave up after the third verse.