cannot for the life of me/him/her/us/them

can't for the life of me

I am completely unable to do something (which is usually stated after "me"). I just met that woman yesterday, but I can't for the life of me remember her name.

See also: for, life, of

Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

cannot for the life of me/him/her/us/them

COMMON If someone cannot do something for the life of them, they cannot do it however hard they try. There is something he should have sorted out, he is sure of it, but he cannot for the life of him remember what it is. I cannot for the life of me understand why you would do such a thing.

See also: cannot, for, life, of

Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012