When I first moved from a big Canadian city (Montreal) to a small American town (New Haven), I realized that unless I learned to dress down, my life would be too complicated. It was way too boring to have to explain every single day that no, it isn't my birthday and no, I'm not going to the Dean's reception, I'm just on my way to the store to buy a sack of potatoes. So I shelved my big-city outfits and learned to fit in. At least, to some extent. (I even went as far as buying a pair of jeans, which is still too traumatic for me to remember.) When my first American Halloween party came up, I was too overwhelmed and depressed by life in New Haven to think of a costume to wear. I decided to go to the party in my regular Montreal clothes.
The biggest and the most fun Halloween party at Yale was celebrated at the graduate students' club. People who came wearing a Halloween costume had to pay $5 for the ticket, and people who came dressed in regular clothes paid $10. When I approached the cashiers, they looked at my Montreal attire and unanimously exclaimed: "That's a great costume! Five bucks from you, ma'am."
During the party, people kept saying, "What a great costume! What are you dressed like?" And I would respond, "Me! I'm dressed like me!"