a word used in reply to combat the mass amounts of "kys" (meaning kill yourself) comments on YouTube made popular by the reaction YouTuber "Pyrocynical". He made a video telling everyone to reply to "kys" comments with "fat" to ensure that this kind of YouTubecancer would be put to a stop.
A word once used to mean "overweight", which has now changed meanings. Now it is used by thin white males referring to their sedentary, lethargic, or just plain lazy life styles.