"""I hate it when the person waits for their turn, then gets out their instrument from the case, tunes it up, etc. "

Agreed, but the same applies to singers, who all too often wait for their turn then start leafing through a folder of songs    muttering "hmm, I wonder what I'll sing" ! ""

So is it more polite to get out / tune your instrument, rustle through your folder,and consult the other members of your group while others are singing?