"look like you're having fun, play mostly correct notes; remember the words. "

...works for me too, but I'll add please not amplified so it can be heard four streets over. Music played really loud has driven me out of a lot of places where I was otherwise enjoying myself. Maybe my hearing's very good (oh lordy, I'll end like my mother: 84 and can hear a mere whisper of gossip at the neighbour's house!)