It's a real phenomenon I've only observed online, luckily not in person as usually people who travel here care about learning about the world. It's not a top 10 tourist spot.
Online examples I've seen plenty of:
- Assuming someone is from the same jurisdiction, especially in legal matters, or asking "which state are you in"?
- Going into a non-US national instance and making one-sentence replies about Democrats and Republicans on irrelevant political matters (most countries like their self-identified republicans)
- Going into a non-US national site and assuming a company name is an American company with a similar name (reasonable, but still an example). For example, we have an NBC, and it's very different.
I think the "Speak English!" example isn't defaultism as much as it's chauvinism. Defaultism seems more like telling them to leave if they don't speak English.