Clever or scary and original are the aims, and generally, the sooner you start planning and brainstorming, the better the costume is. Sadly, if you're looking for a unique Flapper Girl Dress you might need to shop early or they sell out.
Finding one of these fashion gems can be a bit of a challenge though. You can’t just walk into a standard clothing boutique and see a rack designated just for the flapper dress. It’s a rare and unusual item and when you find an original you’ve found a trend treasure.
Some antique stores have a section dedicated just to clothing. You’ll often find some nifty finds here including groovy dresses from the 1960s and bell bottom jeans reminiscent of the 70s. They may have a flapper dress in stock and even if it’s larger than your size you can always have it tailored to fit.
A fun way to approach Flapper Girl Dress to use role reversals. As long as there has been costuming, people have used Halloween to dress 'in drag'; female Charlie Chaplin's and males in mini-skirts. The tradition continues with Flapper Girl Costumes; maybe the female would be a good mustachioed king as her male partner serves as 'his' loving queen.
These flipping abouts don't have to follow gender lines. An accountant's husband could dress the part of a nerd as she mockingly goes as an all-in-black musician. By flipping things around a little, you can get a big laugh.