Don't know if anyone's mentioned this yet. I can't stand it when non musicians or musicians who aren't intending to play occupy seats when there's someone who does want to play who can't get a seat. I was at a session at Cobblestones in Dublin recently where this guy made a great show of plonking himself down in his seat and he proceeded to just sit there for the whole evening without so much as touching his guitar. It was extremely annoying because they were playing some great tunes and I don't get to sessions in Dublin that much. I eventually got a seat, only for this guy from Iran to start playing his native drum right next to me (We're talking bodhran meets very loud tambourine). I was nae impressed.