From the military, it's an acronym for
Taken
Out
Back
And
Shot in the
Head
Usually it's a term to make reference to a person that gets a group into [FUBAR] occurrences multiple time.
> "Ollie! You should be TOBASH! You've gotten this all [FUBAR], your a freakin' [clusterfuck] magnet. We're gonna [deep six] yo ass [bytch]!