Though cookie is really just saying someone is tough ^^

I agree with Rachel. And Rachel is one tough cookie! But, ironically, she is also a softie! ;)

Erm... I would disagree with Jeff. It can indeed be found to be classed as an idiom, and is used for woman sometimes. My understanding of this phrases is that it means someone who won't give up or back down easily, and this is not necessarily a bad thing nor only related to men!

grazie!

A "tough cookie" is a not an idiom but slang to mean a person does not crumble easily like cookies do. It is NOT used especially for a woman. Both sexes apply. There is also another meaning. It means a difficult person. For example, He's a tough cookie, but I can handle him. There was a tough cookie in here this morning who demanded to see the manager.