Maybe its spending my formative years in the deep south, but...ya'll...I feel there are very few reasons to not be nice.
Especially in a professional setting...if you disagree with someone's plan, there are nice ways to express your disapproval and to work together to figure out a sensible alternative. Hell, both of you may learn something from the encounter.
It is not helpful to degrade, shame, or talk down to anyone---a colleague, a trainee, a student, or an employee.
Clearly, this has happened to me, not infrequently. Do I look like someone who will take it? Is it because I am petite? Young (-looking)? Soft-spoken? Female?
I consider working with people---annoying people!---part of my job. I try very hard to err on the side of politeness-- a friendly voice, a smile, a willingness to compromise on the unimportant details as long as the important things are happening. I am getting better at it---I think mothering my boys has helped grow my patience muscle a little, and with time and age I've gained perspective into what really is important and worth getting upset over.
And being nice can yield its own rewards. Work days are more pleasant when you're not wasting energy being angry and rolling your eyes. My overall goal is for people to want to work with me and for me---how would I accomplish this with rudeness?
I wish others took the same approach, I'm tired of self-important big-shots that frequently consult me to help manage their patients (I won't name specialties here) thinking its OK to be an a**-hole.