Stab-Bally Doo Door (pronounced: "stab-bally do-door"): An urban non compos mentis expression of a informal stabbing.

Break down:
"Stab" thrusting a knife or other pointed weapon into (someone) so as to wound or kill.
"Bally" used to express anger, annoyance, or shock, or simply for emphasis.
"Doo Door" is a kiddie slang similar to "doodle". A type of random art work from the toy "Magna Doodle".