Is US defaultism real or a farce?

I’ve seen posts online or memes about it, mainly discussing American people who think the internet as a whole is US-centric despite the topic at hand taking place in another country (nothing to do with America), for example: someone wrote the date format as 30/10/2020 (using the EU format) but some American was like “THE CORRECT WAY IS 10/30/2020” when they fail to realize that user is not American at all.

Is US defaultism real when they travel abroad? They assume the $ is legal tender worldwide in countries where their own currency is used more (the only thing that’ll work is exchanging it but not for direct transactions). I’ve heard an American woman went on a tirade whilst in France as the cashier refused a $20 bill when the prices are in EUROS (WTF?) or being like “SPEAK ENGLISH!” in non-English speaking countries.