If I’m visiting a country it’s usually as a tourist. Even on my business trips I spent half the time being a tourist.

Handling a foreign currency is a lot of overhead, you will only find this accepted in locations where it is quite common for people to not have the local currency. If you're in the middle of Europe you'll have a hard time finding a place that will just accept US dollars outside of some very tourist focused destinations. And even there I'm not sure if it'll work.

The places where I've seen this mostly work was near borders, and it makes sense that you'd accept the neighbour currency there even if it is some overhead. If you can quickly hop over the border you're much less likely to exchange currency before than if you plan a full trip in a different country.

In an increasing number of businesses the UK even if you try and pay in pounds (i.e. cash), they won't accept it. Contactless only!

Doubt. Everyone knows what USD is.

Nah. The "term" USD is common, but that's very different from presenting physical US currency to people and trying to get them to accept it.

At least in Australia, I'd be surprised if more than a single digit percentage of the population would be able to tell if the (US) currency someone presents is real vs pretend/monopoly money.

They'd most likely thing the person is trying to scam them.