This is one of the best drinks you've never had made properly. A great majority of bartenders turn this into a sweet-cranberry juice dominated disaster (or even a searingly sweet fruit punch drink in an up glass). It is most often screwed up two ways: 1) too much cranberry juice or 2) too much Cointreau or Triple Sec. This makes the drink look like a Hurricane or taste too sweet.
If you're a guy and you catch hell for ordering Cosmopolitans, you can give it right back to your friends by using this recipe. It's not a sweet tart and it breaks 40 proof.
First, always use Cointreau (if you like Grand Marnier, go ahead--I'm partial to Cointreau). Do not use plain old Triple Sec. You're using a lot of orange liqueur as a percentage of the total ingredients, so go for the good stuff.
Second, the cranberry juice is mostly for color and just a little bit for taste. The Cosmopolitan should have a reddish hue--that's it! It should be translucent, not solid red in color.
Finally, you really need to shake this one. The best Cosmopolitans I've had have tiny ice crystals floating on top. That's what you're aiming for.
Cheryl Cook, a South Beach, Florida bartender, is credited with inventing the Cosmopolitan in 1985 or 1986. She was tasked with created a new drink out of Absolut Citron. She wanted to come up with a good drink that also looked "stunning". She used Citron, Triple Sec, Rose's Lime, and cranberry juice.
The version we use today was produced by Toby Cecchini who worked at the Odeon in Manhattan in 1987 or 1988. He used Cointreau instead of Triple Sec, and fresh lime juice instead of Rose's (good move there).
The Cosmopolitan really caught on in the 1990s when the girls on Sex and the City quaffed them frequently.