Working with the 'my way or the highway' attitude from advisor My advisor very much has a &quot;my way or the highway&quot; approach in her supervision of students, and chooses to communicate largely through email whilst sitting in her office. Some element of &quot;my way or the highway&quot; is to be expected when someone is an expert in their field (at least in relation to experimental work), but she refuses to listen to any kind of reasonable argument.
Often, rather than coming to the lab, or raising her issues during lab-meetings, she chooses to send emails in person late at night or first thing in the morning such that we wake up to them (she isn't a people person). The emails are often not really related to my project but rather about some aspect of how we do things in the lab. They often come after you've disclosed to her some issue you're having in your work, i.e. my cells died
An email chain may go something like this:

Advisor: I've been thinking about the situation regarding the running of the flow cytometry assays, and decided that XX will run these from now on in your place.
Me: XX's project doesn't require flow cytometry, and XX only works Mon-Wed in the lab which would mess with our schedule. I'm happy to keep on running this, but if you want someone else training to do the assay then perhaps I could suggest YY – they'll be needing to do the assay in a few weeks time anyway and did some work during their masters project.
Advisor: Please come to my office at 0800 tomorrow morning.

Maybe she does have a point. I do need more time in the lab. And could do with not having to spend time running assays.
My issue is that everybody accepts that the advisor has made a stupid decision (we're even sure that she knows that shes made a stupid decision but has taken it too far to back down). The person chosen is chosen not because of their skill/knowledge etc, but because that persons work is currently going well and so she favours them.
Going to her office yields nothing productive other than a re-hash of her emails (she's no more willing to listen to a reasonable argument in person). I don't like having these one-on-one meetings as I end up leaving angry/upset, which damages our relationship generally and makes me want to avoid her as much as possible.
How should one deal with this situation? My gut feeling is to reply along the lines of:

Me: I don't feel that would be productive right now. Perhaps we could discuss this at the next lab-meeting as it effects everybody, or if you're keen to meet one-on-one, then i'd be happy to do so in the presence of ZZ (my co-supervisor).
Given that your advisor sounds stubborn and does not respond well to the students disagreeing, I don't think responses along the lines of 'No, I don't think so' will be productive. In your given example, it seems like the advisor is giving a specific order, and not interested in hearing your opinion on what's right or wrong. 

Your second hypothetical response sounds confrontational and involves using the authority of 'ZZ' against your advisor. Playing off one co-advisor against the other is rarely a productive long-term solution; nor am I sure your co-advisor necessarily is willing to go into direct conflict with your main advisor to help you. 

Instead of responding in the negative, a more diplomatic solution would be to go along with the decision for now and convince them to change it afterwards - nicely and reasonably (perhaps when it is clear the situation has gone for the worse). By being too confrontational, it is unlikely your advisor will be inclined to listen to you in the future. Remember, you are stuck with this person for several years (unless you decide to switch).