Coined by a radio personality in Orlando, TFO'D stands for "Totally Fucking Owsome." (sic) To be TFO'D is to do something Totally Fucking "Owsome," and can be regarded as either a negative or positive thing depending on the context.
Negative: "So the chick turned out to be a dude?! HAHA YOU GOT TFO'D!
Positive: "Dude, you had mad wild sex with a deaf girl!?! HAHAH SO TFO'D!"