I have a few lessons on rehearsal etiquette for a certain oboe player who shall remain nameless, as I do not know his name. We were never properly introduced. In fact, my first contact with him was when he stopped our rehearsal last week in the middle of the piece and said "I can't play with him behind me. You need to move him." Yes, I was standing behind him and singing my solos. And no, he didn't like it.
That in itself wouldn't be so bad. That seems like something we could all laugh about later. The problem was, it kept happening. This guy stopped rehearsal over and over again, for reasons ranging from the plausible to the ridiculous. Any time he didn't like the tempo, he would stop the rehearsal. Any time he felt that one of his colleagues was doing something wrong, he would be shouting to the conductor to stop everything. And he was often wrong.
During one memorable exchange with the soprano soloist, he repeatedly accused her of slowing down her triplets (which she was doing, but on purpose and with the conductor) and causing everyone to be off in an entrance two bars later (which was impossible since she just had two whole notes tied together for those bars and could not be slowing everyone down). The thing was, Mr. Oboe was the one slowing down in those two bars, but he would not hear of it, and in the increasingly heated debate he managed to be quite rude to a lovely young woman in a matter which was really none of his business.
Honestly, it doesn't even matter if he was right or wrong. I totally understand the desire to have everything go well and be awesome, and it can be incredibly frustrating when you are performing with colleagues who are not up to snuff, but there is a time and place to address these things. If you are the conductor, that time and place is in the middle of rehearsal. If you are not the conductor, then shut your pie hole. You are free to mention to the conductor at the break, or after rehearsal, that you think everyone sucks except for yourself, and then that conductor is then free to either agree or disagree, and then makes changes as they feel appropriate.
And I will even give you one interruption. If you really feel that the tempo is way too wrong for you to play, it is within your rights as a performer to ask the conductor to change it. Once. And the conductor can do it or not, but you just can't keep interrupting for the same thing. Nor can you tell singers or other players what to do. Because it makes them hate you. You also might look around and see if anyone else is talking and interrupting. To be fair, different organizations have different cultures, and it might be the kind of place where each entrance, dynamic, and tempo is decided on by committee. But if no one else is stopping the music in the middle of a measure to gripe about the flute player or the cellist, then you probably shouldn't either.
Rehearsals are complicated things. They often involve large numbers of people trying to do something together, and when the kitchen is full of cooks it is very hard to get anything done. The relationship between the conductor and each individual performer is a special one, and if you are not standing in front of everyone else waving a stick, then let the person who is doing that do their job. Like the president, you might not agree with everything that they do, but please at least respect the office.