I agree about the temperament ideas. Dr Berry Brazelton has discussed this most of his career and he was old when I was in my twenties.
I think any behavior, trait, or issue crosses the line in the sand into "disorder" territory when it really interferes with a part or all of life in such a way that there needs to be significant support to the person or they may not be able to develop future skills, live a healthy life or to reach their potential.
Sometimes that's a hard prediction to make, so we just do our best and cover the bases.
