Scottery is something you would say if you wanted to get away "scott-free". This can be applied whenever you say something that warrants a hit. The use of the word would negate the need for a hit. An abbreviation of "scott-free" like scottery can be used in many ways, and its application is broad.
Person 1: Boom nyay
Person 2: Hey, I'm going to hit you for saying that!
Person 1: Scottery!
Person 2: Oh no - he said scottery, therfore I can't hit him!