He told me that I was "a tough cookie to crack." What is this supposed to mean?

[Anonymous]

I was talking to a guy today that I dated not that long ago and things just got complicated and we haven't been talking to each other very often. He told me that I was "a tough cookie to crack" It may be obvious but, what the hell is that supposed to mean? Cause I have no idea.

[coolbeans01]

You were hard to figure out or it was hard to get you to open up about yourself and things around you

[martyfellow]

He means either you are hard to figure out, or you are hard to get into bed. Or, maybe, both?!

[sfauo]

You were hard to figure out.