For a one off coffee sure. It doesn’t matter at all 

But I am confused. Whilst I agree that owning literally anything else as well as Bitcoin, means to some degree you could be longer Bitcoin, a house, a car, gold, could all be sold for more btc

But to say the opportunity cost of using only bitcoin, instead of a less volatile asset (in purchasing power) short term eg eur, usd, aud, gbp, is exactly the same… how do you calc that?

From where I am sitting its not even possible to know what the opportunity cost is, given the unknown trajectory of Bitcoin, let alone say it’s the same