You did not notice that both of your examples have nothing to do with "US defaultism" but just normal properties of shitty humans?

I've heard Britons and Singaporeans speak like this about English, and I've even heard people whose language is not even the "world language" like Germans or Italians speak like that.

Same with the currency thing, I've seen people do that same thing with Euros and Yen.

This is not a US-specific thing, it's just a privileged/narcissistic/patriot human thing.

I mean, why do (some) Americans think that every country uses US Dollars?

Because just like (some) members of every country they’re fucking idiots.

We went to Cabo Verde, Santa María on Sal.

Heard an American loudly proclaim "I don't speak Portuguese" to one of the waiters in the restaurant.

Fair enough. Neither can I, but the waiter was asking for their order in English

Local cafeteria put up a sign that the fish contains bones. I asked about the obvious, someone returned it asking them how the heck he was supposed to eat that, cause you know, it had bones.

I've been to fish restaurants in the US and literally got served breaded fillets. Kinda like fishsticks, but more expensive. Same thing for shrimp, no heads, seldom tails.

The population that is used to eat fish in fishform and shrimp in shrimpform is just very low.

When I was a teenager an American visitor wrote to our biggest newspaper calling us a shitty little 3rd world country for not serving hashbrowns. Which is how I learned what a hashbrown is. I can see why you like them, they're in the same conceptual space as potato chips. Not sure you'll get my buy-in as a breakfast food, though. So greasy!

I feel that the only people who can afford to visit other countries are the stupid, self entitled rich people of the US, so they give everyone a bad name.

Kind of like how the only people who get elected are the stupid, self entitled people so they give everyone a bad name.

I've not seen that level of entitlement at home; I don't think I've seen anyone in person ever say "speak English!" in person like, ever.

You seem like the type that really likes stereotypes instead of depth of understanding and nuance.

I was super young, like maybe 4-5 or something, when my family took a short trip south from San Diego (USA) into Tijuana, Mexico since the border was right there and it wasn't a big deal back then.

I remember seeing price tags and being really surprised... That they were in US dollars.

I don't think I had even started school yet, but I still knew that different country = different language and different money. Not sure how people can miss that so easily.

I mean, why do (some) Americans think that every country uses US Dollars?

Post WW2 the US economy was the only one that hadn't been bombed to absolute shit...

So the US dollar was worth more than any other currency. Exchange rates fluctuated constantly, but US was always worth it. So US travellers could "haggle" in US currency, and even if it wasn't enough at the moment, it might be too much tomorrow.

The assumption in areas with US travelers, was shop owners all kept a stash of US currency to exchange when it was highest.

So you got some elderly travelers who think the world is still like when they were teenagers, and some younger travellers going off decades old information.

For the host country, it's a steady stream. But very few Americans cross either ocean, which is why it's often people on their very first trip who have no idea what's happening. They learn as soon as someone actually explains it, but everyone is so tired of the steady stream they don't keep explaining.

It's the exact same thing with Chinese tourists going to America or Western Europe.

The few who do it regularly, quickly learn to blend in, it's just a constant stream of people who just showed up and have no idea what the actual cultural norms are due to language barrier

Another LLM bot. Same writing patterns as the other ones.

Not exactly an answer but:

No joke, when I was 8 years old, my family left the China for the first time and then I saw some food item in a store in the Korean airport costing something like 15,000 of a currency, I was like holy shit are all foreigners this rich?

Then my dad told me its just a different currency, its actually just equivalent to something like $10 美金 "American Money" (USD)...

Which I also didn't understand what it meant, before that incident, the Chinese Yuan / Renminbi was the only thing I knew of...

So for a while, its was just the adult's weird magic numbers to me lol...

I think some people just never left their country before and never learned about stuff, maybe their parents are also ignorant and never taught them anything.

And the English Language Defaultism probably arises from it being widely taught and so many countries use it like Canada, UK, Australia... and lot of the colonized countries still retained it like India... and its the probably most commonly taught languahe in non-anglosphere countries... So, some English-speaking people just made a false assumption about the world...

One American I knew was absolutely outraged that shops were closed on sun- and holidays.

It's not just Americans who do this by any means, and nor are they the worst offenders! Trust me on this, I'm British - the most wilfully parochial nation on earth.

You'll always get the odd jerk, but mostly this stuff tends to come from a lack of travel experience more than anything else. Unless you've travelled, you may not even realise what assumptions you're making about how day-to-day life works. And, well, a lot of Americans haven't travelled much outside of the USA. (That's not a criticism by the way - the USA is absolutely enormous and incredibly diverse, and you could spend a lifetime exploring it and not see it all.)

All that said, back in the days before dual voltage power supplies were common I did used to find it amusing watching Americans in Europe blithely plugging their electrical goods into the 220V mains and wondering why they blew up.

"Fish and chips por favor."