Passive-aggressive behavior occurs when someone acts in a negative manner despite not openly expressing their displeasure, notes Mayo Clinic. Passive-aggressive behavior may be a sign of mental health problems, but it is not a mental illness in and of itself.
People who are passive aggressive may agree with another's viewpoint, or agree to take certain actions, then act in a contrary manner, states Mayo Clinic. They may choose to make intentional mistakes, feel resentment toward others, or display a cynical or hostile attitude. Procrastination and frequent complaining about not being appreciated are other signs that someone is passive-aggressive. Because these feelings and their associated behaviors can damage relationships, people who suspect they or a loved one is passive-aggressive should consider consulting a mental health professional.