I originally planned on dressing as The Scarlet Witch for the party and was some semblance of the character, I was wearing red and I had a cape. But I did not really look like her. Joel on the other hand made himself an awesome Captain America t-shirt.
Take one blue shirt, measure around the bottom of the shirt (back and front) and divide by 10, add a 1cm seam allowance on either side and cut 5 strips of red and 5 of white. Sew all your strips together, including the two ends and hem one side and then attach it to your shirt. Cut out a white star and affix it to the front of your shirt, stitching around the edges.
Voila! You are done