Some of the greatest rivalaries in history:
Marvel vs. DC. Suit n Tie vs. Shorts n Sandals. Hot sauce vs. Mild salsa. White sugar vs. Honey. The Red Sox vs. the Yankees. The US vs the USSR. Pepper vs. Salt. Ali vs. Frazier. Cyclists vs. Cars. Shade vs. Sun. Fit vs. Fat. Old Facebook vs. New Facebook. White Chocolate vs. Dark Chocolate. Burger King vs. McDonald's. Friday Night vs. Saturday Night. Van Halen with Sammy Hagar vs. Van Halen without Sammy Hagar. Pen vs. Pencil. Dirty vs. Clean. Coke vs. Pepsi. Up vs. Down. Wile E. Coyote vs. The Roadrunner. Nicklaus vs. Palmer. Teenagers vs. Parents. Hulk Hogan vs. Rowdy Rodder Piper. Dallas vs. Dynasty. Star Wars vs. Star Trek. The Munsters vs. The Addams Family. The Union vs. The Confederacy. Mercedes vs. BMW. The Beatles vs. The Rolling Stones. Picasso vs. Matisse. "Football" vs. "Soccer." Elliot Ness vs. Al Capone. Night vs. Day. Cowboys vs. Indians. Cats vs. Dogs. Dusting vs. Vacuuming. Bugs Bunny vs. Elmer Fudd. Glossy vs. Matte. Gum vs. Mints.
And now — October 31st — Halloween — Costume vs. No Costume? You gotta be kidding.
As far as rivalries go, this one's a lame as a wooden duck.
To not dress up on Halloween is most like:
a.) Going to the beach and staying out of the sun.
b.) Going swimming and complaining about getting wet.
c.) Going to a wine tasting and asking for a beer.
d.) Going to a Metallica concert and requesting earplugs.
e.) All of the above.
With 364 days to struggle over what to wear and to worry about how your hair looks, Halloween should be a great day of pleasure and ease. It's the one day of the year that lets you be anything, dress anyway, and act almost anyhow. Who would pass this up? A wooden duck?
With the exception of uniformed police officers, I don't really see any excuse for someone not to dress up. It's friggin' Halloween. 
