I agree with VT, a performer being outright unpleasant or sarcastic to paying member/s of the audience, is bad form (unless they are receiving abuse themselves.) It also causes discomfort to ALL, as we witnessed at Knockers last June with one member loudly complaining about a noisy but jolly crowd of newcomers. Sometimes folks don't necessarily realise they're being noisy, and they can cause disruption without realising it's 'not the done thing' or it's disturbing others. I used to think it was rather rude when people sometimes chatted through other peoples performances, but I got used to the informality of a song session, and realised that it's not a precious environment. It doesn't bother me now, though if I were hearing a very 'light' unaccompanied singer or a sweet little solo on guitar, I think most people would be sensitive to that and pipe down accordingly.
If a performer feels the need to 'silence' his audience, he should either do something stunning which captivates, or at least work out before-hand friendly or amusing methods of communicating to problematic audience member/s that they need to keep shtoom.