Whether you were one in high school or not, everyone is familiar with the stereotypical view of a nerd -- clashing clothes, greasy hair and thick-framed glasses. These caricature-style details make the nerd an easy costume to put together yourself and it's a good choice if you want a group dress theme because everyone will be able to make the outfit easily at home.
Buy a white, blue or checked shirt if you don't have one in your closet. Look in second-hand and consignment stores. Buy or borrow a belt and shoes if you don't have them.
To make the pants, lay the two pieces of 4-foot by 2-foot brown fabric exactly on top of each other. The 2-foot edges are the top and bottom and the 4-foot edges are the left and right. Lie down in the center of the fabric so your ankles line up with the bottom and the top comes high above your waist. Ask a friend to draw an outline around your legs -- take the outline to the top of the fabric to include your waist and torso too. You want the pants to be high-waisted like a geek's. The line should not be too close to your body -- make it about 2 inches wider than you all round.
Cut out both pieces of fabric along the lines that were drawn. Discard the spare material and keep the ones that look like a pair of pants. Sew together the two pieces of fabric along the left outer and left inner legs using the backstitch. Sew together the two pieces of fabric along the right outer and right inner legs using the backstitch. Do not sew up the bottom ends of the legs or the top of the pants -- your waistband. Turn the pants inside out so the rough edges and stitching are on the inside.
Cut the 16-inch by 1-inch piece of brown fabric into four pieces that are 4-inch by 1 inch. Sew a 1-inch-thick end to the top edge of the pants -- line it up with the top edge and do this 8 inches from the left edge of the pants. Sew the other 1-inch-thick end of the fabric to the waistband of the pants. It should look like the loop for a belt that you see on pants. Sew a second one to the waistband in the same way -- this time do this 8 inches from the right edge of the pants. Turn the pants over and repeat to sew the last two 4-inch by 1 inch belt loops to the back of the pants.
Draw the outline of the front of a pair of thick-framed glasses in the center of the card. Look at pictures of nerds, Where's Waldo or Buddy Holly-style glasses online if you need help drawing this. Draw a 5-inch-long glasses arm on the left of the glasses and another on the right. The arms should be attached to the glasses frame so the drawing looks like a pair of glasses flattened out to be two-dimensional. Cut the glasses out. Cut the lens out of the glasses.
Wear your shirt and pull on the pants you made. Tuck the shirt in and pull the pants' waistband up as high as you can, then thread the belt though the belt loops and fasten it. Slick some olive oil through your hair to make it look greasy. Use as much as you need until you're happy with the greasy look. Put on your shoes and fake glasses.
Try to pick a cheap brown fabric such as nylon for the pants if you can. Make the measurements for the pants bigger or smaller depending on your size. Add braces if you have some. If you shop for a shirt, pick the ugliest one you can find. If you have an old, out-of-style pair of glasses, use those instead of making them. Use vegetable or sunflower oil if you don't have olive oil.