Up yurs is the common idiot's way of saying "up yours."

It also means that they literally want to stick something long and possibly attached to themselves up your butt hole.

The use of it essentially means either the user is:
-a homosexual male
-a red neck
-a horny homosexual male
-an idiot
-a female with the desire to test out her new strap-on
person1: "Your dumb"
person2: "well.... up yurs"
person1: *blocks butt hole and runs away*
person1: "DON'T EVER GET NEAR ME AGAIN!
by Silph March 3, 2009
Get the up yurs mug.