Final answer:
The dietitian should stop the line, take the employee aside, and determine whether insubordination can be established.
Step-by-step explanation:
In this situation, the dietitian should take action to address the disruptive employee while ensuring that tray line deadlines are met. The correct course of action would be to stop the line, take the employee aside, and determine whether insubordination can be established. By addressing the employee's behavior directly, the dietitian can maintain a professional and productive work environment.