I'm a U.S. national which makes me a nationalist. I'm not a supremacist, though.
I've travelled to 14 countries on the continents of Europe, Africa and Asia. Then as now, I have admiration and respect for those people, customs, music, food, arts, etc. and appreciate all of the differences between us.
Thankfully, we are not one big boring uniform homogenized world...yet, anyway.
The people of every nation I visited had a perfectly normal and acceptable view of their nation as the best in the world.
And, I think America is the best country in the world.
What's the problem? I wish folks would chill out and simply enjoy the differences and take pride in their own country...or pride in a country they may have chosen to move to. Live and let live.