In American culture, nudity is a big taboo, it isn't socially accepted. A girl I was dating called me a pervert for going to nude beaches and asked me why! I kid you not, I literally got asked why I sunbathe nude. I can appreciate your question, though, if you have been in Germany your entire life it would be difficult to understand why people make a big deal out of it.
Radio show host Tom Leykis has "flash friday" where women are asked if they see a car with its headlights on during the day, to flash their breasts at the car. In America, the fact that nudity and even toplessness are so taboo, that's the gimmick because it's exciting and humourous at the same time. In Europe people would think that "flash friday" is a waste of time, people would wonder "what's the point?"