I used to think I would never parent with "Because I said so." Then I had my DD, and well...

I don't use those exact words, but I often say something like, "I am am adult and have the benefit of many years of experience living in the world that you do not. Based on that life experience, I have wisdom that you do not. I have made a decision. And this is the end of the discussion."

It's important to remember that some kids (not all) find arguing and conflict to be interesting and reinforcing for odd reasons that are not productive.