Yes, it is unfortunate that even at folk/acoustic concerts there are some rude and inconsiderate of others in attendance.

My pet peeves:
1. Loud and inconsiderate people who talk loud and especially those who just cannot refrain from talking loud on their cell phones while the performer is on the stage. It just seems that people cannot be without their cell phones no matter what. I just think it is so rude to talk when a folk/acoustic performer is singing.

2. People who sing-along to the performer's song (when the performer) has not asked for the audience to participate and sing on that song. It actually is very inconsiderate of those around who want to hear the performer only!! If the singer asks for a sing-a-long then that's different.

3. People who stand up in front of you when most people are sitting.
Some people are physically unable to stand at a concert and therefore when someone stands up, and stays standing, it makes it difficult for other's to enjoy the concert. I'm not even talking about someone in a wheelchair (who cannot stand at all) but even other people who cannot stand up at a concert.

These days I mostly just attend house concerts where you don't find these kind of problems.