A megalomaniac is a person who craves power over others and enjoys having it — someone whose sense of their own importance has swollen past anything the facts support. It works as a noun ('the company is run by a megalomaniac') and as an adjective ('his megalomaniac schemes', 'a megalomaniac dictator'). Most often it is an insult rather than a diagnosis: aimed at dictators, at bosses who must control every small decision, at anyone whose ambition has turned into a need to dominate. Cartoon villains who want to rule the world are the standard picture, and the word does carry a faint comic-book flavour, so it can be used half-jokingly about a friend who takes over the group chat. But it also has a real clinical background — describing someone with delusions of grandeur, who genuinely believes they are far greater than they are — and that history is what gives the insult its bite. It is a strong word; used seriously about a real person, it says their judgement cannot be trusted.

誇大狂的人、權力狂（罵人自大到病態、控制欲極強）