Well, I was thinking more of accidental yelling--or situations like MSKKG's(!!!)

but heaven knows, there have been situations where I wanted to whap strangers' kids or yell at other teachers' students. I can think of a period of time where I kept doing this:
The first 6 years that I was on GC, I taught 3 places: at a college, at a middle school, and in a jail. The middle school has strict rules about no gum and the other 2 have none. I would glance up in the jail or college and see a student chewing gum and say loudly, "Hey! Get rid of that gum!" and then remember where I was.