That makes sense in the case where I buy something with dollars, but I'm asking about my coffee for btc trade denominated in dollars example (and I refuse to accept unit of account as an answer).

I don't think the dollar in my coffee example is a medium of exchange. If I was thinking about aggregated trade denominated in dollars but perhaps settled in something else (as maybe most of the statistics we read about in the news actually are in reality) it starts to feel like a unit of account, but still...there is something else going on on the coffee example at least.