Found this on a blog I have been following for a short while now:
In the rather good movie Berberian Sound Studio, an unpleasant film director defines it for us:
Gilderoy, let me just tell you what it is to be a professional. It’s very simple. You cooperate, you don’t question. You don’t argue. You don’t look at your watch. You just do the work you’re told to do and keep your personal opinion where it belongs. Am I clear?