Try putting the capo on the first fret of a flute, getting a clarsach into eight sharps/four flats, or finding a diatonic moothie player who routinely has a G# out and ready.

It helps to understand how the various instruments in the room work. Sometimes you might be in a session entirely composed of guitarists or chromatic button accordion players, more often you won't be.

The kind of rudeness that ticks me off is the opposite - playing a simple traditional dance tune ina roomful of guitarists and finding that not a one of them even attempts an obvious three-chord accompaniment. Most of those tunes were never intended to be played as unaccompanied solos. How hard can it be for somebody to accompany The Mason's Apron or Greenwoodside if they can play stuff as harmonically complicated as Willie Nelson songs? It doesn't matter if you fluff a few bars, TRY.