Per our dr., I am working on some anger management stuff with my child, and one of the main things a person needs to do is identify (themselves) what are the triggers (thoughts, feelings, situations that are commonly problems, etc. ) ...then they themselves can begin to try to catch themselves before it gets bad. For anger management, there's probably few things that work worse than having someone else try to get you to calm down.
I know what you are describing isn't quite anger, but chagrin, at least, and similar self-control measures may work better than being told by others that they're loosing it... (probably there is a book somewhere for this!)
