When you say wrinkle their jeans, do you mean the faded worn lines in the stress areas to suggest that you have been wearing them forever as opposed to the faded areas on the front of the thigh? The lines are often around the crotch, above the pockets and usually some at the hemline at the front of the foot where the jeans would bump over the front of a shoe. Is that the sort of thing you mean? If so it is done by laser. I have seen a video on it. I'll see if I can find it again and post a link.
Kim