When a person with sever flatulence sits on upholstered furniture and the vapor of their farts have permeated the fabric to the extreme that no amount of cleansing or odor remover can remove the smell.
I need to buy a new office chair, because Eddie permafarted on mine.
When someone is considered a permant fag. ie, just like permafrost is somewhere that permanantly has frost, a permafag is someone that is permantly a fag.