Like the above poster I was born in America but my father was born in Italy (and only lived there as a child), I will tell people I'm half-Italian or an Italian-American (also half Franco-American... aka French-Canadian-American, muhaha) often when they hear my last name the subject comes up or people are often curious to what heritage it is, as it's never pronounced correctly if they read it or something (especially when I was in school as a child, I remember every 1st day of a new class the teacher doing role call and insulting me and my last name, then saying something to the tune of "must be Italian?"....
I think it's also because we don't want to say "I'm an American", haha. "Proud to be an American" makes me think of the Civil War and the South for some reason... sorry, just how I think.
The true "100% American's" are ones that have generations of their family tree based here since the 1700's, at least that's how many look at it, and even then they are British, French, and a large mix of whatever (big ole' melting pot here). Whether I'm Italian-American, thegroveful is Irish-American, my buddy Mike is African-American, and my other friend Jason is Korean-American (they like to enforce that they are from South Korea, which a majority are, being that North Korea is as it is), we are all Americans, all people, all the same, and don't view each other any differently because of our differences. But while we don't pay much attention to race for the most part, we are all still proud of our own heritage.
The fact that as a child growing up if I went to a friends house, we'd have "Kimchi and rice" for dinner at my Korean friends (and always shoes off at the door), while at my friend Mike's his mom was new to America (I forget which state of Africa they were from), but she had some crazy good soups and meats on kabobs. At my place, a lot of spaghetti and pasta. Racist? Nope. Just life growing up...
As American's it was understanding these cultural differences, as well as identifying with our own heritage and unique things as a result, but ultimately the first reply nailed it. I'm just explaining it in my opinion growing up in a very diverse culture (Seattle), but of course I guess like thegroveful, all of our parents (friends Mike and Jason parents were both born in respective countries), and became Americans in their 20's.
It's to make us feel special. I am Rocky Balboa, the Italian Stallion, and the true Italian's in Italy can suck it if they dislike the fact those of us in America that are proud to have strong Italian heritage should re-think exactly why (and this goes for all countries, Italian, Irish, Chinese, Japanese, Korean, African, German, French
Notice how you come across somebody once in a while you shouldn’t have f’ed with? That’s me.