Hi Aveline!
No, you are not being unreasonable. I am having the same problem at the moment. I attend a line dancing class three times a week, and think it is so rude when certain people talk while the instructor is trying to teach. I would just ask them to shut up in no uncertain terms, but she is a lovely lady and so far has put up with it.
At yesterday morning's class, 2 women not only talked when she was teaching, but throughout the dances as well! If all they wanted was a chat, they should have gone to a coffee shop!
I thought it was me being touchy, but other people have commented, so it's not just me. My friend says to just screen them out, but that's easier said than done. Grrrr!
xxx