2) Originates from the movie/musical known as 'Sweeney Todd'. In this movie, Johnny Depp plays the role of Sweeney Todd, a barber that slits peoples throat while giving them a shave.
3) To Sweeney todd someone, you would have to kill them in the same manner as Sweeney Todd himself of an alternative way that is just as horrific.
2. to slit the throat of an unsuspecting victim by a straight razor.
3. to hide the crimes by butchering the corpses of victims, baking their flesh into meat pies, and selling them to unknowing customers.