Other people call Bitcoin a "Pyramid bubble"
Wikipedia
A Ponzi scheme is a fraudulent investment operation that pays returns to its investors from existing capital or new capital paid by new investors, rather than from profit earned by the individual or organization running the operation. Operators of Ponzi schemes usually entice new investors by offering higher returns than other investments, in the form of short-term returns that are either abnormally high or unusually consistent. The perpetuation of the high returns requires an ever-increasing flow of money from new investors to sustain the scheme.[1]
When a Ponzi scheme is not stopped by the authorities, it sooner or later falls apart for one of the following reasons:[1]
The promoter vanishes.
Satoshi Nakamoto vanished
The differences between a Ponzi scheme and a legitimate business are actually more subtle than people realize. When a public company makes enormous profits and those profits are not invested in the infrastructure, financial responsiblities, or growth needs of a business then that business collapses. We don't call those types of businesses Ponzi schemes but in fact they are no different.
The simplest and most obvious Ponzi schemes are when the owner of the funds makes zero attempt to actually manage the funds in a legitimate fashion, he spends the money on what he wants. These type of Ponzi schemes always collapse when the investors ask for their deposits back and a run on the fake bank ensues, exposing the scheme.
Bitcoin is an investment only supported by 1) actual usage of the coin as a transaction medium and store of value 2) investor confidence that the controls in place can secure that value
Both of these attributes are almost non-existent in any Ponzi scheme. #2 for a little while, but there is no way for Ponzi sheme's to recover if #2 ever collapses.
Bitcoin has one other magic bullet up its sleeve that makes it almost eternal, barring a world ban and barring world war, that magic bullet is that regardless of the value you place on Bitcoin, you can always buy it and sell it for the current market price. Ponzi shemes don't have this eternal nature and it is what makes Nokamoto's disappearance irrelevant. He can sell all of his bitcoins if he wants, so can the FBI. The price may go down to 10 dollars, but the market will still exist, as will the users and the people that are now willing to buy in at $10.
You might better describe Bitcoin as perpetual bubble wave whose end of days is correlated to the end of humanity.