The first year I went, a woman came by, looked at the empty seat next to me, and asked me if I knew what I was doing. I told her I'd sung Messiah every year for the last five years with a great choir, so she deigned to sit next to me.
I can't blame her, it's no fun sitting next to someone who isn't singing, especially as a soprano that sometimes screeches. Somehow it's ok if we're all screeching together, but if the person next to you isn't singing, not so much. There was a woman talking at intermission this year in the restroom. She said that she was sitting next to three people that weren't singing, and the guy next to her made a face and covered his ear when she hit a particularly high note. Kind of takes the fun out of it, you know?
One year I got a seat towards the front, but I was irritated because there was a young boy with an obviously brand new score sitting down the row from me. Great, someone who won't sing, and will grimace when I hit lovely notes. And where are his parents?! I fumed until we started to sing and the most glorious sound I've ever heard came from his direction. A boy soprano.