noun. The essence of something that spooked the horse, shit the bed, and soured the deal.
Real citation: "Nothing else in his answer confuses us away from this first sentence. In response to a direct question on the dealbreakerness of carve-out personal accounts (the only ones worth debating), the president used the word 'voluntary' in the first sentence. And it's hard to be murky on this: carve-out personal savings accounts vs. add-on accounts is a black and white issue. Because of the way the SSA pays benefits, either all of us accept carve-outs, or none of us. Add-ons can be voluntary, and voluntary is the key word."
(Michael, April 29, 2005, http://rosettaweblog.blogspot.com/2005/04/i-must-have-missed-something-part-2.html)
Made-up citation: "When dating, cats have the stench of dealbreakerness for me, because they make my lungs shut down, like adorable, furry Darth Vaders."