GTFO is an acronym for the rather rude term "Get The Fuck Out". It is normally used more when someone is surprised than when someone wishes for you to please exit the room in an expedited manner before the can of whoop-ass is opened and the dogs of war are unleashed, thank you.
The acronym came about from early forums like the old AOL chatrooms and continued on when texting on cell phones became popular. Shortening the phrase made it easier for lazy people to get their point across without all of that typing, pecking, and grammar.
Iron Noder 2017