Stands for BeaT The Fuck Up.
This phrase is uttered when a party or person does something totally inappropriate or absurd in someones point of view.
In a sprint race, someone tripping an opponent near the finish line.
Calling someone something out of line within a group of people in an argument where all parties comprehend the gravity of the statement towards the affected person.
Rosie O'Donnell, Danny Bonaduce, and Flavor Flav all got a TV show. Which in turn is BTTFU.