Referring to the act of violently attacking someone, generally with a bladed object. Coined from the main character in "Sweeney Todd: the Deamon Barber of Fleet Street". This phrase is often used in a blustery manner with no intension of actually engaging in violence. It can also be used as an expression of anger.
1. If my boss doesn't lay off, I'm gonna go sweeney on his ass.
2. Seriously man, I'm so pissed I'm getting ready to go sweeney.