Sentence examples for fat cats from inspiring English sources

'fat cats' is correct and usable in written English.
You can use it to refer to affluent people in a humorous way, as it plays on the idea of cats being well-fed and content animals by figuratively applying the phrase "fat cats" to people who have a lot of wealth. Example: The donations to the charity came primarily from fat cats who had more money than they knew what to do with.