I had to yell at a special kid today.
Why did you have to yell at him?
Because I had to display my authority.
I'm sorry, but that's not a valid reason to pick on a special kid.  You can find other ways to do so.
I know, but he needed to learn a lesson not to act in ways he shouldn't.
I think you know that it wasn't right to yell at him. If he needs to learn to behave differently, it should be a teacher or a parent who communicates kindly how he should make changes, not you yelling at him.