Tone, here is a different point of view, that guy gets pleasure from singing those songs, furthermore here is a quote "old timey musicians make their singing and music appear effortless because they sing their material over and over".
I would rather have a performer who sang three songs well than a performer who is unfamiliar with their song and hides behind a bloody crib sheet, it is the crib sheeters of this world who are bringing the music down, mumbling away and performing badly.
answer,you just put up with it.

why not tune up your guitar in a different room or ask him nicely can i just have a few seconds to tune up.