This code indicates displeasure not so much with the person as with the performance. There is the suggestion that the person is talented and could have done much better.
This is an assessment code. It is a strategy very frequently used in domestic disputes because it simultaneously praises the person's ability and condemns the expression of that ability in action.

A parent who expresses disappointment with a child's performance in an examination implies that the youngster 'could have done better' if he or she had tried harder.