Back in the early 1970s when I left the land of my birth to travel 'out' to Canada, the language of Empire still ruled our thought processes. While Britain was handing off its colonies as fast as it decently could, the mindset of POSH - port out, starboard home - remained ingrained in the way we spoke about the world. Indeed during my seven years in the 1980s running the Canadian subsidiary for an old-established English firm, my UK colleagues with international responsibilities referred to any trip offshore, including to the old Dominions, as "going out to territory". By then I had developed some sensitivity to local attitudes, and, try as I might, I could never persuade a single one of our frequent visitors from HQ to consider how condescending use of the 'out' phrase sounded to their offshore-born colleagues.
My American counterpart, British like me, had an even more frustrating time reigning in the terminology of his head office visitors. Our main office down there was in Concord, the birthplace of the Revolution. This colleague and I had periodic meetings with Joe, our worldwide Chairman. At these discussions in a local Massachusetts hotel bar, as the brandies consumed increased in number, Joe would loudly defame the locals' manners and mores using his rich Yorkshire vocabulary. Joe's two great national dislikes were Yankees and Germans. Germans after all had started two terrible wars, and Americans only came in on the right side after the real work had already been done. Unlike his American counterpart, our CEO in Germany could not claim to be British to dodge our Joe's contempt.
British postage stamps still do not carry the name of their country of origin, presumably on the basis that Britain invented this method of paying for mail. US businesses (as the 'World's Only Superpower') rarely put 'USA' at the end of their address nor their country code in their telephone number.
Such little slights are the things that can antagonize foreigners; unfortunately they don't teach you that in school where you are (or were) a Top Dog country.