Step 1: Use a seam ripper to remove all of the embroidery on the first t-shirt. This took a VERY long time, so if you're working with a similar top then I would highly recommend pulling up your Netflix queue...
Step 2: Cut the second t-shirt into horizontal strips. The width is up to you; mine probably ended up being about 1.5 inches wide.
Step 3: Gather the strips to create ruffles. You can do this by hand or by machine.
Step 4: Arrange and pin the ruffles onto the first t-shirt, however you'd like.
Step 5: Sew the gathered edges of the ruffles to the first t-shirt. I would really recommend using a sewing machine for this step.
Step 6: Trim ruffles as necessary. If you'd like, you could trim the edges with pinking shears or a decorative pair of scissors to add interest.
Finishing touches: Finish up the project by taking up the shoulders a bit and removing the drawstring from the bottom of the t-shirt. Voila!