This is a matter of your personal preference. There is no right or wrong to it, but here is my opinion: The topic is how instructors project themselves to their students during lessons. On the one hand you can say how they come across is simply an extension of their own personalities, but teaching— like being a public speaker, a news anchor, or a TV weatherman—is a learned skill. As a teacher you have choices, and if you are self-aware, you can hone your communication skills be whatever you think works the best.
Two extremes aggravate me when I hear of them or watched in person. An instructor is presumably a professional. Patience and understanding by definition are part of the job. Some of the things which I have heard an instructor do or say in a lesson are too offensive, unkind, or inappropriate to go unchallenged. If an instructor feels that he or she is above working with a novice student, then they should decline the job, not complain and not be mean. Years later someone whom I taught in the past has recited what I had said to them back when. In our profession we must be mindful of the impact our words have and how long their effect can linger!
My other gripe is almost a polar opposite. It is instructors who are not honest with their pupils. Let’s be clear—it’s all right to have a sliding scale. “Relative good” or improvement should be rewarded even if the result is not anywhere near “absolute good” yet. But c’mon, people, an endless stream of “be-YOOT-ifuls!” and “su-PERS” delivered with false enthusiasm shouldn’t fool anyone.
As I said, this is just an opinion. If you are charmed by either of these modes, more power to you. If you teach, however, it’s worth listening to yourself occasionally to see if you fall where you mean to along this continuum.