How do you want to earn your respect as a teacher? An angry teacher will strike fear in the hearts of their students. A calm teacher will ideally just be an unshakable individual regardless of how you interact with them. I need to give you a little more detail.
This angry teacher isn't merely angry, but this teacher also expresses their views through sarcasm and openly questions the intelligence of their students. Think in the long term. This angry teacher consistently expresses their level of disapproval, their sarcasm, and questions the intelligence of their students. This angry teacher doesn't necessarily commit to these same acts with the same student all the time, but there is definitely at least one student who suffers this wrath. This teacher's students go home everyday remembering their teacher's behavior because it is exhibited everyday. Worse, there are often students who will overemphasize the representation of this angry teacher's behavior. But, the parents don't necessarily know this and just take their child's word for it. Fast forward to parent teacher conferences. Will the parents of these students be more or less inclined to take the advice of this teacher? I propose that they will be less inclined.
Now, take the calm teacher. Whenever a child forgets to bring homework, talks in class, doesn't have the necessary supplies out, this teacher says nothing about intelligence, does not necessarily express disapproval, but just says, such and such expectations were not met. During recess, you will need to complete your homework, practice not talking to a neighbor, having your supplies out and so on. Worst case scenario, this child tells her mother or father that she lost recess time. The parents can ask why and it will be because a student wasn't meeting a class expectation. That child lacks the ammo to make some wild story about their teacher's character.
The bottom line that I'm trying to lead you to is that an angry teacher will more readily get themselves in trouble with parents than a calm teacher will. When your options are to have the parents support or oppose you, don't make it hard on yourself. You have no reason to and so no one has an excuse to be the angry teacher. You'll make life easier for yourself as the calm teacher. Don't give parents a reason to complain to you to the principal.