I agree, rude (or worse yet, uninterested) listeners can be bothersome, but I agree with Sean, in that the audience is the key, and reaching people is why most of us do this (it sure isn't for the oodles of cash we all get).

The other problem I see is (and forgive me for saying this) is that there are more than a few performers have problems with projection and no voice training. This not so bad when you're mic'ed and have instruments backing you up, but on a cappella pieces it can be deadly for the performer because very few audiences will strain to hear every word and note of a set, no audience wants to hear a performer search for a key and nver find it, and worse off, it will make the job of the next person trying to perform that much harder, because most people seem to have a once bitten, twice shy approach to new music. I'm not saying we all need to have PHDs in Music, but I think any stage performer needs to have enough training to be able to support themselves, and the music they're doing.