not knowing idioms

haven't (got) / don't have a clue

ex : i haven't got a clue how to use this camera

: meaning

i don't know at all

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haven't (got) / don't have the faintest idea

ex : i don't have the fain test idea where she lives

: meaning

i really don't know at all

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haven't (got)/don't have the foggiest idea

ex : i don't have the foggiest idea what this switch is for

: meaning

i absolutely don't know at all

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can't for the life of me

ex : i can't for the life of me remember her first name

: meaning

i can't remember at all

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be a bit out of touch

ex : I'm a bit out of touch with computers these days

: meaning

i used to know about them,but don't know the latest developments

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doesn't ring any bells with me

ex : I'm sorry,that name doesn't ring any bells with me

: meaning

I don't think,I've ever heard it before,it is unfamiliar