I'm amazed that everybody on this thread thinks *beginners* are the problem. Round here it's usually people who might have been good 30 years ago but have lost their voice, memory for the lyrics, taste and sensitivity to other people before almost all the current club-goers joined. You can't tell them anything.

In contrast, there is one really crap instrumentalist I often encounter who really *is* a beginner (and has been that way for 10 years) but seems much less problematic. He *knows* he's not very good, he puts a lot of effort into it, and he keeps his spots short and to the point. Everybody I know likes him.