I quite frequently walk into pubs with my guitar and just start singing - sometimes you can have a good session - other times you get told to stop. Anyway I walked into an interesting looking pub one summers evening and realised that they had a band (folk-ish) booked already - it was during the interval. I bought a pint, and as it was warm and the pub was quite packed, I walked out into the garden carrying my guitar. I barely got out of the door, when I was grabbed by a couple of guys who thought that I was stealing one of the group's instruments. The landlady was called, and a member of the group confirmed that my old yamaha didn't belong to them. "Can you play it ?" asked the landlady. I did a couple of songs before the group went back on, and got a gig for the following week. I've played there many times since.