The idiomatic expression "to feel like a king" means to experience a sense of greatness, importance or power. It is an emotional state where one feels on top of the world and as if they are ruling over everything with absolute authority. This phrase can be used in various contexts such as when someone has achieved something significant that makes them feel proud, confident, and invincible; or it could also refer to a person who is living lavishly and enjoying all the luxuries of life like royalty.