Get an oversize shirt. I got a mens shirt. White with black print.
Lay the shirt down face up and make incisions about 1 inch apart on the sleeve. Start at the bottom, and cut about half of the sleeves length. Work your way up to about 2 inches from the collar.
Do the other side with the same amount of cuts, so it hangs even when finished.
Now , from the bottom of the shirt, make horizontal cuts towards the center of the shirt. Make the first few cuts the same length ( you'll cut the bottom off later) then start to make them shorter towards the top of the shirt. Stop about 6 inches from the 'armpit' of the shirt. Again, note the amount of cuts you make and the distance. Using a tape measure or ruler is helpful.
Try the shirt on. Its going to hang low so cut the bottom to where you want it to stop.
Lay the shirt down flat and even so one sleeve is face up, and directly above the other sleeve. On the front of the shirt, make incisions starting from the bottom, and getting shorter towards the top. Cut as much as youre willing to have your stomach show through, basically.
Do the back. I made mine a bit shorter than the front. Making sure the collar is even , cut a neckline. Start shallow, you can always slutify the vneck later ;]
Cut off the rest of the collar, and make incisions on the top back where the tag is, similar to the bottom cuts. ( starting long and shortening with each cut)