I highly recommend using a pair of spandex free jeans. To find my perfect pair, I headed out to one of my favorite local thrift stores and picked up a pair of Calvin Klein, high waisted and kind of "mom-ish" jeans for $1.99. I wanted the fit to be good at the waist and hip but also a little loose through the thigh.
CUT AND DECONSTRUCTION:
1. I used a pair of shorts (that are a little on the longer side) as a trimming reference. Turning the jeans inside out and laying them out flat on the ground, I put the existing shorts on top and marked the length with a piece of tailor's chalk. With a pair of very sharp shears, I proceeded to cut off each of the legs. Ideally, you want there to be a slight angle on your cutting line. The measurement should be a bit longer at the crotch than at the hip. Also, make sure to not cut through the pockets.
2. After cutting off each of the legs, I tried on the newly shortened jeans to check for length. Remember, these are going to be frayed and therefore will be a bit shorter than how you originally cut them. You can always trim them up a bit more so make sure your first cut isn't too extreme...unless, of course, that's the look you're going for.
3. As these jeans were "pre-loved", I didn't have to do much in the ways of breaking them in. If your's a little more on the stiff side, try giving them a once over with some sandpaper. For my shorts, I used a razor blade to make a few slits slightly above the edge of the new hems. I made a total of approximately 8 cuts (front + back) of varied lengths and heights. Make sure not to make cuts too far up on the back side (for obvious reasons).
4. At this point, if you're happy with the existing color of your shorts, toss 'em in the washing machine on the "heavy duty" cycle. Check for results and possibly wash once more. Dry on low heat. Wear and enjoy.
If you are not happy with the color of your shorts, or if you just get overzealous (as I was), look below to see how I bleached my denim.
This was actually my first attempt at bleaching anything that wasn't hair or white linens. I am actually pretty proud of the results. I wasn't going for a splattered or whiskered look...I just simply wanted an allover lighter color.
To do this, I filled my bathtub with enough hot water to submerge the shorts (approximately 1.5"-2" full). While filling the tub, I mixed in some bleach. The more bleach, the faster and more extreme results. Lay the shorts flatly in the tub avoiding the existence of any folds, creases, etc. With gloved hands (or some sort of tool), submerge the shorts making sure that everything is evenly soaked. Check on your shorts periodically, occasionally turning them over and agitating the fabric until you are satisfied with the color. Mine ended up being in the tub for a little over an hour. Remember, wet fabric (like hair) is going to appear darker than dry fabric. Once your ideal color has been achieved, drain the tub and rinse the shorts a few times with cold water. Wash in the washing machine as instructed above. I ended up running mine through the washing machine twice (once on heavy duty and once on regular) to help get rid of the bleach smell. Dry the shorts on low. Wear and enjoy.