What is Tear You A New One?
1.
literally rip someone a new asshole.
in use can be verbal abuse or a threat to actual physical harm or in some circles could be quite literal
see
you better stop lookin at my girfriend before i have to tear you a new one
2.
Among the highest degrees of complete ownage, to tear someone a new asshole is to either physically or verbally beat the living fuck out of an opponent or his or her arguments.
Jon: I'm so much bettter than everyone.
Me: Is that before or after I tear you a new one? Let's see...together with your girl parts, that'll give you three
See
3.
Kicking someone's butt.
If you don't quit looking at my wife's hooters dude, I'm gonna tear you a new pronto.
See