"Let's try that posture again so we can see how you can avoid hurting your neck." This is the best answer, because this is this the nicest way for Randall to inform his friend of his bad posture without discouraging the friend.
Step One: Define the Problem: “What is the problem?”
Step Two: Identify the Causes of the Problem: “Why is this happening?”
Step Three: Brainstorm Possible Solutions.
Step Four: Select the Best Solutions.
Step Five: Implement the Plan.
Step Six: Follow-Up, Evaluate, and Monitor Progress.
Simple google search. Hope this helps.
