How much Japanese do you know?

Not a lot.

I know that although chotomate kudasai  is a very polite way to ask somebody to wait a moment, choto-bloody-mate works just as well. And it's faster.

I know that if you can't pronounce do itashimashite, "don't touch my ashtray" will get the message across.  And "Monday night" is a fair substitute for mondai nai, which means "no problem".

And I know that if you can't be bothered with the whole rigmarole that follows O genki desuka? You can get away with saying "Pretty genki, thanks."

And I figure that, while yosh is the Japanese word for "OK", yoshi doshi  must be close enough for  "okey dokey". 

And I know that the closest you can get to my name in Nihon-go is Ebanzu, which sounds surprisingly like "Evans". (The final 'u' is silent.)

But of course, I'm only a gai jin so I'm scarcely an authority. >:-/

Of course, that's all written in Romaji. I wouldn't have a clue how to write it in Hiragana or Katakana, much less Kanji.

nothing much.... I know only greeting words like

kon'nichiwa.

I've learnt it since grade 5, but I'm not close to fluent.  I can read and write all hiragana and katakana, and I can recognise about 30 kanji.  I know a LOT of verbs, and basic sentence structures.  My friend can speak fluent Japanese, as she lived there until she was 12, and she speaks it at home.