I know someone who genuinely believes that he's limbering up his fingers when noodling, and that its a good thing to do!!!! Doesn't realise at all that everyone is politely waiting for it to develop into something.......
Same person has been known to cut across someone elses (admittedly slightly hesitant) start of a song with a jaunty "right - I'll do one then."
Some people are just oblivious!!! I know that its not intentional, and that they'd be horrified if they did realise what they were doing. Which is why I'm too chicken to take the bull by the horns & explain. Which I suppose makes me the bad person really........ - but how on earth do you explain what they've done without making them so embarassed that they never dare come out again?

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