Download the PDF file, and print onto medium-weight 11-by-17-inch paper. (If your home printer won't use that size of paper, most copy shops will be able to print it for you; simply put the file on a disc or a thumb drive and take it to one.)
Cut the paper into a triangle by cutting from the corners of one end to the center of the opposite end (use a paper trimmer or a craft knife and a metal yardstick or long straightedge).
Paint a 1/2-inch dowel white or whatever color you want. The paint will seal the wood to avoid splinters and will provide a washable surface, as well as create a polished look. We used an 18-inch-long dowel, but most lumberyards sell dowels up to 48 inches long, which would make a very tall flag.
Attach the wide end of the flag to the dowel with double-sided tape, and tie on a ribbon bow.
Vest, shirt, bow tie, and shorts from Crewcuts by J.Crew.