No, a psychologist cannot ethically diagnose someone with anything they want without talking to the patient first. Diagnosing mental health conditions requires a thorough and professional assessment, which typically involves conducting interviews and gathering information about the patient's symptoms, personal history, and current circumstances.
Ethical guidelines and standards, set by professional organizations like the American Psychological Association (APA) in the United States and similar bodies in other countries, emphasize the importance of informed consent and the establishment of a collaborative relationship between the psychologist and the patient. This means that psychologists should discuss their observations, potential diagnoses, and treatment plans with the patient and obtain their consent before making any official diagnosis.
Diagnosing mental health conditions requires a careful consideration of the patient's unique experiences, context, and personal perspectives. Therefore, it is essential for psychologists to engage in open communication with the patient and involve them in the diagnostic process to ensure accurate and comprehensive evaluations. Making diagnoses without proper assessment or without involving the patient would be considered unethical and could harm the therapeutic relationship and the patient's well-being.