idiom about knowing nothing

[Puru Muru]

If you want to say that you know nothing about something, is there some idiom in English for it? Something like "I know neither night nor day about it", "I know neither earth nor sky about it" or anything similar, or not similar?

[BobK]

'I don't know the first thing about it'; I've also heard 'word one' in place of 'the first thing' in an AE context; I don't know how widespread this is.

Also 'You could write what I know about that on the back of a postage stamp.'

b

PS Also, but this is pretty obscure, when someone asks about something you can refer cryptically to 'a blind ungulate' - think about it: /nǝʊaɪ'dɪə/

[5jj]

We also, informally, say that we know f*** all about something, shortening that to F.A. or sweet F.A. if we are faint-hearted. We can also know b*gg** all or so* all about it.

My genteel use of asterisks suggests that you do not use these expressions yourself. Some find them offensive.

More acceptable is I haven't the faintest. The word idea at the end is often omitted, as it was there.

[BobK]

...

More acceptable is I haven't the faintest. The word idea at the end is often omitted, as it was there.

I've also heard 'I haven't the foggiest'.

b

PS Your first bit, with all the asterisks, reminds me of a '60s satirical programme at the time of what was known at the time as 'The Cod Wars'. There was a song that ended with the words 'In fact they got Rockall.' (It was a fairly inconsequential disagreement - Cod Wars - Wikipedia, the free encyclopedia - that involved among other things disputed ownership of Rockall - Wikipedia, the free encyclopedia )

[birdeen's call]

Puru Muru, try this: know - Idioms - by the Free Dictionary, Thesaurus and Encyclopedia.

[JMurray]

If you don't want to admit that you're completely ignorant on the matter, it's very common to say "I know next to nothing about that". But it's fair to say that the person you're speaking to will probably assume you know b*gg*r all. Fivejedjon, I hope you don't mind me adjusting your slight asterisk excess (gee, that's hard to say). In these parts "stuff all" is also popular.

[5jj]

Fivejedjon, I hope you don't mind me adjusting your slight asterisk excess

Not at all. I am not an asteriskiser (?) by nature, and got a lttle carried away there. I think b*gg*r is more pleasing to the eye than my version.

[Tdol]

And we have pig ignorant as well.

[Barb_D]

And this lovely double negation:
You don't know bupkis.

(You could use a more standard "You know bupkis" but I like the double negation better.)

[BobK]

That's a new one on me. We do have [the possibly related] 'bumpkin' - a person who combines naivety with knowing bupkis. (which often* appears in the 'urbanocentric' [not an established word as far as I know - I think I just invented it] slight 'country bumpkin').

b

PS *I just looked in BNC. There are only 14 occurences of 'bumpkin', and 9 of them are preceded by 'country'; of those that aren't, several have a strong implication that the bumpkin is 'not from the town' - e.g.

'5 H8S W_fict_prose A B C fact that I've never been to England before doesn't make me a complete bumpkin . Athens is a capital city too, you know. Honestly, you Londoners...
8 AHN W_newsp_brdsht_nat_misc A B C with a modern metropolitan's contempt for his own country's traditions, but a bumpkin 's ignorance of economics...