To unlock this perk you need to overcharge your armor to 200. I guess there is several places in the game where this can be done. However, I found a good spot in chapter 4. It is in the tavern after you meet Annette.
TheOdd101 said:
I did the nightmare level just before this and when I finished I came out with 75 armour, if this happens to you, you have to wait for the dog to jump through the window take its armour after you kill it and very quickly run to each piece of armour.Any questions? Feel free to ask.
Good luck! :)