Crocodile was a woman!
You remember this guy
he got his ass kicked by Luffy and lost his position as a Shichubukai. As I'm a bit bored atm I'm posting a theory about this croco-crackhead.
My theory is he was a....
Why do I think that? Well he has met Ivankov a long time ago when he was still a rookie, which was just a bit after the years of Roger's execution and as a result of this meeting Ivankov knows a weakness of Crocodile. I believe this might be that Ivankov knows he was once a woman. Though this is more of a secret than an actual weakness. If it would be what Ivankov meant he should have formulated it differently. However even if it's not that, I still think it could be directly related to it.
This is backed-up by the fact that Crocodile was witness of Roger's execution, just like most of the other Shichibukai, but he was the only one of whom they didn't show his face, only his back unlike Doflamingo, Mihawk and Moria:
You can't even see whether he has long or short hair and considering Ivankov can change people's gender and he was a rookie at the time they met, he could have changed gender while no one noticing it.
...yes I made this on a whim, though I'm partially serious about this >.>