@XXSpadeMasterXX,
It's interesting to me if it's interesting to you. A couple of disclaimers, though: First of all, just because I spent a year as a monk doesn't mean that I'm an expert. I'm sure some of my understandings are wrong, and I'm trying to root those misunderstandings out all the time. Second, what I say does NOT represent mainstream views held by Buddhists in general. Some of what I say is my own ideas; some of it is from scholars of Buddhism, like Richerd Gombrich, Mark Siderits, Sue Hamilton, etc.
Unskilled behavior is defined in the suttas as any behavior that doesn't lead you toward the goal of release, liberation, seeing things as they really are, or if you prefer, Nibbana/Nirvana. Some things are held as universally unskilled, such as killing, stealing, lying, improper sexual relations (adultery, rape, etc), and a few others. The rules that the monks/nuns follow are only conventions, not moral laws.
So, yes, we can see some unskilled behaviors in others, but not all of them. Sometimes, what can be unskilled for one person can be skilled for another one. Only the individual can know whether or not some behaviors help or hinder that particular individual. Chanting, for example. It can help clear one's mind, or one can be so attached to it that it becomes an unhealthy obsession, preventing him/her from pursuing more productive practices.
It's almost entirely about trial-and-error and self-correction, therefore some of the most important meditation training is mindfulness meditation. Paying attention to what you're doing, what you're thinking, how you're feeling, what your habitual responses are, etc. If you notice a habit to become angry in such-and-such a situation, it's up to you to recognize it and try to break the habit. You can get advice from others, but you still have to do it yourself.