But if I take my fiat and convert it to cash, I can use it as toilet paper. You can't do that with BTC.
I don't know what you think when you use the "convert" word here

If you convert fiat into cash, I can also exchange BTC for cash, what is the difference? Can BTC still be used as toilet paper in a different way? Just kidding

I think that's called
intrinsic value 
No way, can't think of a better way to call it

So what is the intrinsic value of Bitcoin? Can I call the terrible volatility the intrinsic value to bitcoin?

A historic ~49% range in a single 40-minute candle.