There is no such thing as constructive criticism. In relationships criticism is actually destructive. If one is critical in a relationship, the individual is putting down their partner. The skill in relationships is to move from criticism to feedback.
Criticism points out a partner’s inadequacies or flaws. For example, “You are such a critical person.” The focus is on the partner rather than the experience of the individual to the partner.
Feedback is when a person shares their experience. For example, “It upsets me when you tell me I’m a bad parent.” This individual is expressing their reaction to their partner’s statement.
This is the reason “I” statements are much more effective than “you” statements. “I” statements tend to focus on an individual’s experience whereas “you” statements typically focus on a partner’s deficiencies.