One of my fav zombie movies is "Shaun Of The Dead" and I printed off a free online stencil at Stencilpunks.org on an old pair of sweatpants to create an Halloween worthy garment.
To make your own, grab an old garment and either fabric paint and roller sponge or other brush or a bleach pen (I used a bleach pen on these), freezer paper, an iron and an X-acto knife to create your own spooky slacks or terrorific tee.
The stencil can be found over at http://www.stencilpunks.org/ under "Movies" the scroll down to find the Shaun of the Dead Stencils.
For further details on using creating a freezer pencil stencil, see the following.
Happy Halloween crafting!