As an ethical person, I feel it's my obligation to sit quietly, out of the way, and without moving around while my opponent is shooting.
The only things I say to an opponent during a match is "your on two", "was that a foul?", or "that's a foul", and very rarely I'll say "wow, nice shot". That's it, and I can't really think of anything else a person should be saying to their opponent during a match.
When you are almost never talking to your opponent during a match does it really matter if the other person is wearing headphones? You want to tell the other person they are on two? Make eye contact and hold up two fingers, they know what you mean.
For the people who apparently like to chat a lot during their matches, I guess all I can say is YOU are one of the reasons why I wear headphones