Of course I checked online after I'd read your post, and found these definitions.

Now, I'm quite an old guy, and so any slang that I'm familiar with is likely to be turning into history. However, I have a 22 year old son and so I checked with him. He wasn't able to give a definition for either expression so I conclude that they are not in common use in the UK.

My feeling about slang is that it can be fun and can be interesting, but I don't worry too much about it. When I lived in Chile I resisted spending too much time on Chilean slang because it isn't universal and I knew I wasn't going to live in Chile for more than a year. Slang that is universal is a much better use of time.

I have absolutely no idea what you mean.

To white fang? Boo?

I come here to learn things that nobody I've ever met has ever said. It's like an anthropology class.

I'm glad to be spreading some amusemet around!

I was being humorous, but it's also true that I do learn about other varieties of English here. When I teach English I have to ask myself if a slang word is worth introducing to my students or not. Often I decide that it isn't.

I suppose if we have enough curiosity about the world, we are all, always in an anthropology class.

"White fanged"... Interesting. Sorry for the off-topic answer but may I please ask you where you encountered this expression? Is it from a series or something? I've read the book but had to read the explanation to get the meaning so I just wonder if anyone who hasn't seen the series that google refers to would understand it.

I've heard "boo" a lot because I spent the better part of a decade surrounded by American college kids, both as students and friends. They said "boo" a lot, to talk about their boyfriends, girlfriends, but also jokingly with close friends. I never used it because slang feels very unnatural to me. I always feel like I'm playing a role when I slip in a word.

This is the first time I've ever heard "white fang" though.

By the way, Phil's comment about feeling like he's in an anthropology class made me burst out laughing. Except that I feel like this most of the day, whenever I go.