You are only liable for CGT if you sell an asset (= realised gain).

So, if you buy a stock at $10 and it goes up to $100, your CGT liability is a certain percentage of $90 ($100 - $10) upon liquidation.

If you buy a stock at $100 and it goes down to $10, you end up with a $90 (generally carry forward, some jurisdictions allow carry backwards) loss that can be used to offset other gains.

yes - but isn't that what's essentially happening here when you run your coin thru a mixer and mix it with other coin (which must have the same value) - you sell your coin and get back a new one with today's value - voila a taxable event ....

I would assume you would argue that you merely moved money (or assets) around, just like you would wire money from A to B. Moving stocks with unrealised gains from broker A to B is also not taxable.

The only person you would ever have that conversation with would be the IRS (or your local tax authority outside of the US), and they are bound by confidentially.

yes but that act of mixing your coin with others effectively gives you back mostly other people's coins .... what's their value if not today's value?

If I go get change for $10,000 in $100 bills and ask for all $1's do I realize 10,000 dollars in capital gains because those are "other people's dollars"

but they're dollar bills, the currency we pay taxes in, they're always worth $10k no matter what happens to their actual intrinsic value ... a better example is:

I buy 10oz of gold for $1000 (this was a while ago), this week I exchange my gold for a different 10oz of gold (less a small commission to the exchange) currently worth $10,000 - is that a taxable transaction? I suspect yes