You know what phrase is strange? "One tough cookie".
Why a cookie? When cookies get overdone I wouldn't describe them as tough. I can't think of any situation involving cookies in which I would incorporate the word "tough". I would be thinking more along the lines of crispy, or blackened, or crunchy.
"He's one crunchy cookie."
That just doesn't have the same ring to it, does it?
It would make more sense to say, "He's one tough steak," or something like that. Don't you think?
"He's one tough piece of leather."
"She's one tough Kevlar suit."
Just a passing thought as I was clearing the dinner dishes tonight...