I saw a review of this book on a blog and thought I'd take a look. The presentation is incrediby tacky.
Internationalization of urban English is a great idea, only this book doesn't do much more than provide explanations of some spicy set phrases. Some are translations, but from what I could see, there were also probably real Japanese equivalents that could have been provided.
Of course, there is a long tradition in Japan of relying upon set phrases books, so that's not a problem. The main problem is that this book plays to one stereotype of how SOME African-Americans talk. It MIGHT help someone understand, perhaps, what is said in the movies or on hip-hop websites, but doesn't empower anyone to relate to real people.
If an unwary Japanese person actually tried to use the phrases in the book, s/he's likely to get into real trouble. Context is everything, and so is age group. Not much of the book would be of any use talking to someone not of the hip-hop generation, and nearly all of it would be considered extremely rude, not "hip." Further, Japanese in polite society wouldn't understand or be able to use much in this book without embarassment. The author probably needs a punch-perm consultant. Had they put the Japanese-equivalent of the rough-neck wannabe on the cover (motorbike, punch-perm, stylized sneer), it probably would sell better, because it's all about image.
Conversely, if an African-American person got stuck in a Tokyo subway, nothing in this book is likely to help.
In short, this is a fun book, because the phrases are set and voyeuristically funny. However, it is unlikely to be useless for real conversation.
It would have been better done as a website.