idiom about knowing nothing

[BobK]

PS Puru Muru: if it's a man you don't know, you 'don't know him from Adam'.

b

[Raymott]

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?

If you don't understand something - say a movie or a speech - you can say, "I couldn't make head nor tail of it."
That's close, but it's for 'understanding' not 'knowing'.

[birdeen's call]

As a Pole, I must love the etymology of the word "bupkis": bupkis - Wiktionary

[Puru Muru]

Thanks for all!
The question arose because an Estonian idiom, literally "I know/understand neither night nor sky about it" has changed in the youth slang into "I know/understand neither night nor hat about it", and it was assumed that the reason for the change was the example of an English similar idiom. My opinion was that there is no such example and it seems that I was right.

[BobK]

I think you're right.

Other alternatives that haven't been mentioned yet:

I don't know squat (or an alternative word that uses the same beginning and ending letters)
I haven't a clue/Not a clue / No clue (this last has a bit of an American tinge to my ear)
That's a closed book to me
(The subject needn't be 'I' in any of these cases.)

b

[Tdol]

As a Pole, I must love the etymology of the word "bupkis": bupkis - Wiktionary

It has a charm.

[missiebarcz]

Puru,
None that I am aware of here in the US. Odd that it changed from sky to hat.
Missie

[probus]

"I haven't got a clue" is common. It also has the virtue of being neither pejorative nor profane.

[Khosro]

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.

Well ! I know what f*** is but I have no idea what b*gg** is !

You sure have seen "fuck" in the dictionaries. It's not written as f*** there because they are means for teaching and learning English but they also say that some find it offensive since mentioning politeness or offensiveness is also part of teaching and learning a language.

My point is I am against writing fuck and other similar words with asterisks because here we are learning and teaching English. We are working with words and sentences and here fuck is a word just like any other word.

[birdeen's call]

I have no idea what b*gg** is !

Link.