What was the stupidest form of US defaultism you've encountered in real life whilst they're abroad?

I've heard of a case where an American man was ranting about "why can't they speak English" despite him being in a country where it's not even spoken (in this case: Japan), like WTF? He's literally in another country where a different language is spoken, isn't that already common sense? Yes, there are (some) Americans who are like this: assuming that everyone all over the world just knows English from the get go, but that's not always the case.

Another was when an American woman wanted to pay for the bread at a French bakery using a crisp US$20 bill, but that was not accepted since France uses Euros as their main currency. I guess it stems from the fact Mexico accept that assuming that's universal in countries where their own currency (like the Korea uses Won, UK uses the Pound, Oman uses Rials & etc). I mean, why do (some) Americans think that every country uses US Dollars?