A bullet-proof kink is one that 'gets you' every time you read it, that pushes your buttons. You'd stay up until 1am reading a fic that contains one of your bullet-proof kinks, even though you have to get up to go to work in four hours. *g*

Example, one of my bullet-proof kinks is possessive sex with marking (such as biting) and claiming. Love. It. Give me Don throwing Charlie up against the wall and biting his neck, or giving him a hickey... *melts*

Does that help? (Or was it just TMI? *g*)