Unfortunately for said shock racist, noone laughs.
A shock racist is generally not a racist all the time and will only break out with slurs at the most akward, unfunny times.
John (talking about Ryan, who is black): Haha ryan is such a n*****
Brad: Dude that guy just saved 3 children from a burning building
John: I know what a n*****y thing to do
Brad: fucking shock racist...