I think that is what has irratated me most when playing at a party or whatever, when I start losing their attention. It happens at gigs, or small parties. Keeping audience involvement is hard. It's not easy to keep yourself from thinking, "Why am I even here?" . Probably dialing in the demographics of the crowd quickly, by trying different sets, and mixing the songs up, detirmines what mood they're in. If they're in a raunchy, drinking rock/blues mood, and you play a country ballad, they will light up cigarettes, grab a beer, and talk all the way thru the song. Only clapping when the song is over, because of habit, not because they even heard any of it.