Theatre etiquette

I hate when I'm rehearsing a show, and someone decides to bring a friend along to rehearsal with them. When you're still developing your character, learning music, or choreography, there shouldn't be people not involved with the show around. You end up making a fool of yourself during rehearsals a lot, and you don't want people to witness it. True, the rest of the cast is there watching and listening, but they all go through the same thing as you, so it isn't a big deal.
Tonight, someone brought a friend along. I was not happy about it. I would have said something to him about it, but in the 3 and a half hours we spent learning choreography tonight, I really didn't have much of a chance.
Granted, none of us have had much time for a social life the last few weeks because we rehearse 6-7 nights a week. Bringing someone to rehearsal could be an opportunity to spend some time together. The cast should have been asked before someone was brought in. Don't be fooled, I would have said no if I was asked, but we weren't, which is just poor manners. I'm still a little pissed about it if you can't tell.