Dont get angry.

To be angry with a weak person is proof that you are not very strong.

As a leader its your responsibility to give affirmative effective and adjusting feedback. Even if the person disagrees with the feedback, never get angry.

Not getting angry does not mean you cant give feedback around your disappointment or disapproval.

Always Smile. You cant get angry while you are smiling, you can give adjusting feedback on behavior while smiling. If you feel yourself no longer smiling, stop.