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.
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.