Talking while people are singing is bad manners. If a friend or two are over and we're working on something I expect others who drop by to be quiet. If they ain't I say something once and then ask (tell) them to take it outside. I had someone once who said, "But it's freezing out there" to which I replied "It'll be colder than that in here if you keep flapping your tongue."

At a playing gig it's my responsibility as a performer to keep the audience quiet. In other venues/situations, if the proverbial loud-mouths keep talking I quit playing. Life is quite simple in some regards.