First off, to make the dye, you will need 2 bags of coffee grounds (About 10 oz each), preferable Espresso.
You'll need some old stockings or pantyhose to use as a filter for the dye.
Add boiling water, and let the java brew for a little bit.
Finally, drop your denim jeans inside, and let the color take. The end result really does vary according to just how dark you like your coffee...or jeans.