I know that apparently, some American travelers put Canadian flags on their luggage or carry on then claiming they’re from Canada (the dead giveaway on debunking this is their passport, since how can you be “Canadian” when you have US citizenship unless you’re a dual citizen in possession of both nationalities) since some of them have hatred towards the US or feel ashamed of the country due to its internal affairs.
Yes, I have several friends who did it even 20 years ago
They weren’t fully trying to represent legally that they were Canadian or hate the country. But backpacking / doing hostels across Europe they generally did get treated better and didn’t have to get into arguments about US policy and things. Especially once the Iraq war and stuff got into full swing
People were doing it 50 years ago too.