Don't ya hate that when you gotta go pee and somebody stops you!yeah...wait to talk until the break between bands, or before or after...
and sooooo many people will come up and want to have a full on conversation.
On rare occasions, when stopped by a very persistent drunk, I've successfully ended the conversation by abruptly saying "Oh no! You hear that? The PA is about to feed back! Gotta run!" 99% of the time, people at gigs are actually nice... albeit a little buzzed.