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1.
(verb) To kill somone with a straight razor via the jugular vein.
Im about to go Sweeny Todd on your ass if you ask me again!
by Assassin Phone inc. April 07, 2008
 
2.
1) Cockney rhyming slang for the Flying Squad, an elite fast response dectective branch of London's Metropolitan police. Often contracte to The Sweeny.

2) A mythical and murderous London barber who killed his customers and sold the bodies to a near by pie shop.
"WE've been told to touch nothing until Sweeny Todd get's here."
by black flag June 26, 2004