I see that everyone here have nice "my own theory on something" time so now is time for mine speculation.
Having lot of time without new chapter made me thought about Vergo and what we have seen/heard from him and If Im right he didnt took any damage from "non haki" attack beside Laws "counter-shock"(yes, I think that Sanjis DJ kicks are enchanced with haki, same like Luffys Red Hawk). So there must be a reason for his durability.
Vergo acted weird few times having problems with his memory, some people said that maybe he is some kind of cyborg but I think that he is metal/ iron/ titanium/ some other heavy metal or simply metal man.
Poisoning from heavy metals causes person to have problems with memory, even personality disorders. So maybe he is somehow like Magellan- poisons had its tool on him even while he was poison man himself, still he was attracted to his DFs "element". Vergo after coffe with Monet and Cesar said that coffe and cookies were good but then they said to him that there was no cookies, before going after SH, G5 and Law he was searching for his sword just to be reminded by Monet that he is not a swordsman later while talking to Doflamingo he said something about taking pics of Law after he finishes him off with camera he bought at Dressrosa and Doflamingo says that he didnt bought any camera there.
We saw that Sanji said that his body is like big chunk of metal and we all thought that it means that he was using Tekkai- there is possibility that we should take Sanjis words literally here. That would somehow explain Sanjis bone cracking while tanking one of Vergos heavy kicks.
This might even explain that food sticks to him, when you are cooking food doesnt stick to teflon for example but it often gets stuck to metal. People now might think about that spoon that got stuck to Vergo face, well I know its streched but some metals after getting some electricity migh get a little mangetic, he was at laboratory so..
Thats why I think that Vergo was thinking about next day and his breakfast when Law stuck him to fence instead of acting like he was going to die. Before he get to know that Monet is going to blow everyone(erm..) he didn't seem concerned at all. I sure hope he didnt die with smile on his face like one of D, he is not worthy of this kind of death.
It will probably not became true but I like my theory
I did some more reaserch- Vergo said once that Hamburger is his favourite kind of food, so I googled "heavy metals hamburger" and it seems that I found something very interesting- hamburgers/ beef often contain lots of heavy metals.
http://www.yearofplenty.org/2010/05/...ef-supply.html
I dont want for my post to get enormous so just read about problems caused by too much heavy metals in ones diet.
http://www.meltdown.com/metals.htm
I will just quote first few lines
"A single mother called my Meltdown hotline and requested a Tissue Mineral Analysis for her and her daughter. The daughter was doing terribly in school. She couldn't remember her multiplication tables and was failing math. The funny thing was, the mother was having trouble remembering things, too."
Now I like my theory even more