Naff--my new favorite word

Mark Satchwill, my arty other half at NoHo Noir, introduced me to this word, British slang (I learned from Urban Dictionary) for "lame." 
Naff. It's my new favorite word. I don't understand why it never caught on here in the US, where sillier words have become common currency.
I've been thinking about words a lot lately, specifically slang, because late last year I tried something I'd never done before--writing a story set in swinging 60s London.
I would have felt more comfortable if it were set in 1860s London because there's more of a margin for error and it's not like someone is going to pop in and say, "That's not what we said!" (Well, there are sharp-eyed people who know the 1860s inside and out who would probably let me know if I got it wrong, but you know what I mean.)
It's really  hard to be persuasive writing about another time and another culture, and I have a horror of making a misstep especially since I tend to get snarky about writers who don't do their research and get things wrong.  (You know the kind of thing I mean--novelists who describe the fields of white marble crosses in Arlington Cemetery not realizing they're describing Flanders Fields and not the garden of stone that is the nation's most-storied national cemetery where all the tombstones are tombstone-shaped.) And language is the trickiest thing.
I have several friends from France whose English is superb--nuanced and slangy and grammatically perfect. The only thing that marks them as non-native speakers, besides their accents, is that instead of saying "last night," they say "yesterday night."
Which reminds me (yes, I know this is a NAFF segue) of a story I once read, probably in EQMM. Set in WWII it was about a German spy who was caught because when he spoke (in English) about the moon, he referred to its gender as male.  That's the kind of thing I mean.
Naff.