My first reaction is to yell at them in public, and tell them exactly what I think is wrong with them or what they're doing. This is almost inevitably unhelpful to anyone, as the hostility and caring too much makes people get all defensive and steel themselves against anything related to what's said. It seems that a lot of the time, the most effective way to get the point across is to be detached, to simply not give a rat's ass whether one's advice is taken seriously or not, and to try and say what needs to be said with as little ego as possible.
Is it empty talk, the old saying that tact keeps you whole?
When truthfulness is complete, it still resorts to this.