Things You'll Need
Needle and thread or sewing machine
The codpiece first came into fashion during the Renaissance. Men wore tights that only covered their legs, and they risked exposing themselves when sitting or riding a horse. Costume codpieces do not have to serve the original function, only provide a bulge on a man's costume. You can make a simple codpiece using a thong and a scrap of fabric, which can be worn over or under your clothing depending on the needs of your costume.
Cut a triangle of fabric that is two to three times larger than the triangle on the thong, depending on how large you want your codpiece to be.
Fold 1/4 inch of the triangle's sides back to hide the cut edges. Cut a small notch in each corner to allow this.
Pin the triangle to the thong with straight pins. You will have to gather the edges of the triangle somewhat to make it line up with the smaller thong.
Sew the triangle to the thong, leaving a 1-inch gap at the top.
Stuff the codpiece with polyester batting.
Finish sewing the codpiece shut.
Decorate the codpiece as required by your costume, using sequins, beads, glitter or whatever other materials you want.