Having recently been to Japan, I can say with some assurance (and credibility) that this whole "fuckin sale" is actually more than meets the eye.

There is a tradition in Japan to buy pretty little bags (or purses) for Japanese New Year. These bags are called fukubukuro, or "lucky bags". Add one more letter, a "c", and the English-speaking Japanese population (most of them) get a chuckle out of it.

It isn't about Japanese people just thinking american slang is awesome; it's about being clever enough to play on both languages for something each side will appreciate (unless they're easily offended).