What you will need:
I bought this top from gap, for literally $3 (apparently in-store has better deals), and bought some white fabric spray paint from Michaels.
Fold an 8 1/2 X 11" sheet of paper into a triangle, and cut off the excess. Fold the triangle in half. Cut on the two sides the have the folded crease. I chose to cut a large, simple design because my shirt has tiny small lines. This is the fun part though- cut a few and see what you like best.
I also chose to use matte white to make sure my design would show up enough on my semi-busy shirt. I put a piece of cardboard in-between the shirt. I got really excited, and rushed through the fabric spray paint process, and therefore ended up with some extra paint on the sides.. don't do that. Have patience and tape off or use another sheet of paper to block off the sides.. and Finally,
The finished product. Minus the sloppy paint on the side, I love how this turned out. I have a short sleeve neon pink t-shirt that I think would look cute with a silver design.