"Worst thing" is subjective, really. What bothers me might not bother you, and vice-versa. I've been called some bad things "professional-wise." I've been called some bad things "personal-wise." Really depends on what irks you. For me, the professional comments hurt b/c I try very hard to be ultra-professional at work.
A few years back, my section head said something to me after he saw me chew out my shop for them screwing up. He said "You know...when you lose your cool, your shop has no faith in your abilities as a manager." And he just walked away.

This guy was one of my mentors so I took his comment to heart. Turns out he was right.
You NEVER lose your cool in front of your subordinates. You can praise, punish, chastise, reward or just show no reaction...but you never lose your bearing. Don't lose your cool.