What does a person do when school is canceled because it is too cold out? Study for upcoming exams? Of course not! What kind of person do you think I am? Exams don't start for three days! Instead, I pulled out an old t-shirt, and decided to try and spice it up. It should be know that while I am reasonably talented when it comes to creating new things, changing old things is definitely not a skill of mine. So, I set out on this adventure.
Materials: Scissors, if you sew, the little ones and the big ones. If you don't sew, nail scissors and kitchen scissors will do.
Old t-shirt you don't mind potential ruining. ( I recommend one that is form fitting but not skin tight.)
A very large safety pin ( mine is around 4 inches long and half an inch wide)
The shirt started off looking like this:

Step 1: Cut the sleeves off. I opened up a bit of the sleeve (pull the place where the two pieces meet, and take the small scissors and snip the threads that attach the two pieces), the used the big scissors to cut just inside the seam (on the body side).
It should look sort of like this:

Step 2: Decide whether the shirt looks good like this. I advise trying it on, because it looks very different on. Mine was too loose under the arm pit, so I decide to continue.
Step 3: This is where the safety pin comes in. Take the shirt off, and gather the material in the back between the arm holes together, secure with safety pin.
I think this picture will make more sense:

If you have questions, please ask in the comments, I will get back almost immediately.
Enjoy!