@Ionus,
I was pronouncing it U-Es-Ay -ee-ans everytime I read it.
I call myself American, but that doesn't mean that I don't think anyone else who lives in North, Central or South America are not allowed to call themselves American if they want to- the terms is open to anyone who wants to use it, I'd say.
I think the reason it is used primarily by people who live in the USA on the North American Continent, is because people from Mexico say they're Mexican - people from Brazil say they're Brazilian - people from Canada say they're Canadian- they reference themselves by the country of their birth - and as far as I know - the United States of America - is also commonly known as America and that is the country of my birth. That's all I mean when I say it.
I have never used the word 'sofa'. I use the word couch.
I also never say, 'We're having a barbecue' - I say 'We're having a cook-out.'
Which means the same thing - we are cooking outside on the grill.
I do use barbecue as a noun - as in the sort of meat marinated in barbecue sauce and slow cooked that you get in North Carolina or Texas.
One idiom I got from my Mom and Dad is: help your plate or fix your plate,' and people - even in the north in America (or sorry, the USA) where I grew up would say, 'Help my plate? Fix my plate? Is it broken?' and they'd look at me so strange. I was saying, 'Please feel free to choose the food you'd like and put it on your plate.' I think this is an idiom specific to the south.
My mother used to call every refrigerator a 'frigidaire.' We would just laugh at her.