The phrase "being fat city" is an outdated slang term that is used to describe a state of prosperity or success. While it may have been popular in the past, it is no longer commonly used and has since been replaced by a variety of other synonyms. Some of the most popular alternatives include being in a good place, being on top of the world, living large, thriving, flourishing, doing well, being flush, and having it made. These phrases are more modern and better reflect the current state of the English language. Regardless of the phrase used, the sentiment remains the same - success, abundance, and prosperity.