Interesting - I'd heard of American Gen Zs using theatre to mean the art form, to distinguish it from just meaning a building, but I hadn't heard of British English being considered a more prestigious register than American English. Is this a new phenomenon?

I don't think OP meant "arrogant" in terms of more prestigious, but in the sense of any native US-English speaker using British English spellings as a way to seem fancier or more formal.

Non-native US-English speakers are not viewed in the same light (in my opinion).

I find there are a few specific Britishisms (like theatre) that don't really raise an eyebrow in the US and maybe can seem a bit more upper-class. Grey vs. gray are essentially interchangeable. Toward vs. towards is another.