Why Americans consider nudity a big deal?

I am European and one time I was walkin in the park with my American friend and it was hot so I took off my shirt. He was very wierded out, and felt akward, he was like "you are so Euro, do that when we go back to cl :)". And like I never see naked babies and naked little children when I go to the beach. (Now your American mentality is telling you: he is a pervert, molester, he should be hanged, but no I'm just Euro). When we were kids we didn't put swimming suits until we were 5. And girls didn't put the top part until 8-9 (they have nothing to cover). But yeah in Europe nudity is not a big thing, I think, it's more like a funny thing.