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Tourist:
Just about everyone owns a Hawaiian shirt. Add some Bermuda shorts, a visor, a camera (or two) around your neck, and sandals on your feet (socks optional). For a funny effect, stuff the butt of your pants for that extra-dorky look. Find or make some brochures and tickets to stuff in your pockets and you're good to go!
Gypsy:
Wear your funkiest colors. Girls: layer two or three skirts on top of each other, with a peasant blouse and lots of jewelry. Guys: wear loose pants tucked into boots, with a shirt unbuttoned to reveal several gold necklaces (plus a vest if you have one). Wear a scarf around your head and another around your waist, and boots on your feet (or just go barefoot).
Pirate:
Start with a bandana around your head. Boots are very helpful but you can make boot tops by wrapping dark fabric around your lower leg flapped over at the top. Women--wear a skirt with a ragged bottom. Men--either tuck some loose pants into your boots, or cut the bottom into a ragged edge. Wear a loose shirt unbuttoned at the top, with a vest (it's easy to make a vest by cutting up an old shirt). Wrap a piece of fabric around your waist for a belt.
Cowboy:
Everyone owns jeans, and chances are good you own some kind of western or plaid shirt and boots. If you can get your hands on a cowboy hat, that's great. Accessories like a gun belt, lasso, bandana around your neck, chaps or vest add to the look.
Nerd:
Easiest ever. Just wear your clothes a size too small, with your shirt buttoned all the way up, and pants pulled up too high, over white socks and Grandpa shoes. Add a pocket protector, fake zits, and gel in your hair to make it look extra-geeky.
Sandwich Costume Idea
Buy two square pieces of white foam, cut into the shape of slices of bread, and darken the edges by dipping them into watered-down brown dye. Make sandwich fillings (cheese, lettuce, etc.) out of felt and attach to the inside of the front slice. Hang the slices over your shoulders with straps. Top it off with a decorative toothpick hat.
Idea submitted by CarliJ
Photo submitted by BlcBery