How do you explain this?

http://www.youswear.com/index.asp?language=Japanese

Fakku? That's a transliteration from English. Most Japanese speakers generally agree that Japanese doesn't "really" have any of its own swear words. Yes if you get technical there are some like those listed on that site, but generally there are not, it is a very polite language.

Try calling your female Japanese friends "manko" and see if you still have female Japanese friends.

Please see my above comment. "generally agree" and "Yes if you get technical there are some" and "but generally there are not"

You just picked out one example. That defies my definition of generally?

In my experience the public face of Japanese society is very polite, but that's distinct from what can be said with the language, and what people say with the language in private face contexts. It also varies to some degree by class, but you could say the same thing about English.

Also, loanwords like fakku are a legitimate part of the language. The katakana script is used almost exclusively for them and many sentences have them, spoken and written.