A razorblade or scissors are the most direct ways to make holes in your jeans, though you could stick a stiff wire brush on a Dremel rotary cutter, stretch the fabric taut, and grind holes in it.
Why am I telling people how to ruin their jeans? I have no idea, but if you want wrecked-up jeans, you could take a job at FedEx as a "package handler" and load trucks all night long. Pretty soon your jeans would look like they'd been run through a food processor. Ask my husband about this.
For your viewing pleasure, here are some repairs I've made to my husband's shredded work jeans:
Example 1
Example 2
Example 3
Example 4
Example 5
These were some big, gnarly holes that took a lot of patching and patience. These are also not jeans my husband wears anywhere that he wants to look especially suave and put-together.