Then how about paying after ordering and eating a meal?

Depends.

If there was a posted notice that no cash is accepted it's unlikely you'll get a criminal charge, but you can get civilly sued. Most places will just accept the cash then put up a picture saying "If this asshole shows up again, trespass him"

You're being more literal than I was. My point was that "a debt" is a broader concept than the GP comment acknowledges. A debt is incurred any time you propose or agree to buy something. And legal tender is the way you settle it.

I was making a joke.

But also, I think that most people would not consider any debt to be incurred for transactions where the payment and receipt of goods is done at the same time, like in a grocery store.