I won't get into specific patients (I'm not a doctor but work in health care) the worst patients in general is an older person with untreated borderline personality disorder. They call screaming their heads off that the medication they've been on forever is giving them side effects, and it's just that they have this void within them that you can never pour enough attention into. They're obnoxious, demanding, and treat people in an ignorant fashion as if you are a servant at their disposal, and if you don't answer them right away they start threatening suicide. The younger ones with BPD are largely at least somewhat aware and are calmer and just sad and tearful, but the total dysregulation of the older ones is a hell of a thing to see.