I have never yet found it a problem.
guest AW,who recently went to one of my gigs,stated that he found someone else singing along with me annoying,this is a fair comment.
every audience member who is at a club or a concert does need to consider the other people present.
I was at a seated concert some months ago [cinema type seating],and had my concert disturbed by someone who needed to go out for a smoke every 20 minutes,so I had to stand up and let them pass four times.