Most flipped refers to the highest number of times an object or concept has been turned over or inverted. The antonym for the phrase most flipped would be least flipped, indicating an object or concept that has been turned over the fewest number of times. Least flipped could also refer to an object or concept that has never been flipped over at all. In the world of real estate, most flipped refers to a property that has been bought, renovated and sold quickly for a profit. An antonym in this context might be a property that has not been flipped at all, or has been owned by the same person for a long period of time.