Professionalism is kinda a weird thing. People sometimes put a distinct separation between professionalism and fun in anything remotely resembling a business, as if you can't be good and organized while still having fun with your friends. It's primarily brought up when a hard decision has to be made, as if making the touch decision in a negative manner is important to being professional.
With my experience with The Originals as my primary reference, I think that being professional means being organized, being proactive, not letting your emotions get in the way of you work (though it can be a healthy supplicant) while still keeping the experience fun. Organization increases the quality of life for every, so everyone has just a little more room to explore, grow and be happy. Even while working with different ensembles, at the end of the day you want people to feel like they have succeeded but know what they need to improve on.
Now, there will be tough decisions on occasion, but what makes you a professional isn't making that tough decision to hurt others, passionately fighting for either site or even playing devil's advocate all the time; when a bad situation presents itself, sensitivity and humility are essential. What makes you professional is being logical while being very aware of people's emotions. This way, you can convey what you really think and not be afraid of retribution because you're being smart with your wording. It's so essential to always stay calm and see things from everyone else's point of view. Make whatever you do about the others, not just yourself. Have protocol for everything so you're not guessing all the time and so people many years from you can continue to learn from your teachings. These things are all what being professional is all about.