My only experience of intolerance at sessions is hearing the mutterings of the sessioneers when a dozen or so naked bassoonists loudly descend en-masse, barge everyone out of the way and start smashing the furniture and beating the chunks of mdf on the walls without waiting for the singer or musician to finish. If it continues like this at the Coach and Horses in Barton-Without-Hyphens, someone will eventually have to say something.