When people, if they happen to remember to, reflect on the notion that the country they happen to have been born in just happens to be the greatest country on earth.
Why not celebrate by going to Twitter and and reading the back and forth under a hash tag called #AmericaNeverWasGreat. There are a lot of liberal people and a lot of conservative people on Twitter and the idea that people can actually consider the notion that America never was great really brings out conservatives' patriotism, if by patriotism you mean vile, seething hatred of liberals, and gays and commies and Blacks.
The topic, or hash tag, is "trending" now, meaning lots of people are tweeting, or posting about it, maybe because it's Nationalism Day and people are pissed off about displays of nationalism they're seeing, but it's been on Twitter for awhile and apparently was a reaction to Donald Trump's campaign slogan "Make America Great Again."
Meanwhile, I saved this from somewhere on social media awhile ago: