Piffy wiffy means that you're so pissed off and cannot tolerate people's bullshit anymore, or, the person at hand is having a very awful day and needs to let off some steam.
jon arbuckle: "Garfield did you eat my lasagna again?"
Garfield: "No, what makes you say that Jon?" Garfield says as he cleans his lasagna-covered cat mouth.
Jon: "GARFIELD, YOU MAKE ME FEEL SO PIFFY WIFFY AAAAAHHHH." as Jon shouts he slams the door behind him in a fit of rage.