Personally, I think it is incredibly rude when people try to talk to you when you are obviously playing your guitar. Can't they wait at least til the song is over? Next on my list of pet peaves is when you're playing something cool and people start making stupid requests. Say you're playing a classic Dylan tune and they ask if you know any Jim Croce. Give me a break!

Oh, and to answer the question, I can't talk to people and play at the same time. I usually ignore them or stop playing if what they're saying is important.