I am sure this is the bane of all sessions.
At our ECWS events there will be a session in a local pub or round a fire and a guy used to play a guitar but he used to drink as well somtimes at the same time as his booze level went up his ability to play went down.
On night the guitar was even more out of tune than usual. There was a realy good accapella session going and off he started one of the group got up took the guitar and wound the strings off the tuning heads saying "sorry I am a music lover". At the next event our guitar playing friend took along a recorder,whistle and harmonica.