Hm, isn't "f you money" an amount that allows you to give your boss the finger and stop working? I think the term you are looking for is "couch money" I'm fortunate enough that paying an additional $10k isn't really an issue, but I enjoy watching money grow in my investment account almost as much as driving a fast car.
Having FU money is when you tell your boss to shove it because you don’t need their paycheck.
FU money to me is “being able to speak your mind freely in any and all situations”.
Elon is a perfect example of that. He can wage war against the SEC, British expats in Thailand, and make 420 tweets to impress his girlfriend.
Elon just needs to realize his employees and his retail shareholders might not have FU money and can’t afford black swan events being Musk himself to torpedo their holdings.
$10K can always be deployed elsewhere for better use. It’s tough to figure out the demarcation point between wise spending and living a little.
Personally, I think a good goal for that is when you are either debt free or have low enough debt at low interest that doesn’t stress your family.