If you’re AUSTRALIAN - Say G’day to the fly, get rid of the coffee and head down to the local 
A Jamaican would take a nap.
If you’re Greek- you yell, “Eureka!”
If you’re swiss, you take out the fly and fondue it in chocolate. Sell chocolate fondue to tourist as “Protein Enriched.” Sell remaining coffee to some other tourist, for a Franc more than the usual price, touting it, too, as “Protein Enriched”
If you’re a squid, save the fly and the cup of java til it’s time for a crossing-the-line ceremony. Usually for several months. Then feed the properly fermented cup of Posiedon’s Draught to some unsuspecting 'wog. Laugh like mad when he pukes. After all, the other shellbacks did worse to you…
If you’re Norwegian, you’ll just wait a few minutes. You already know you drink your coffee strong enough to sterilize and then dissolve the fly before the coffee gets cold, and wasting coffee? Why, that’s almost sinful.
Unless you’re a trønder, in which case you will take no chances, and pour in some moonshine just in case. Alcohol is a good sterilizer, you know 
ewww, Noone 
If you’re far-sighted you yell: “Darling, I found your contact-lens”
If you’re near-sighted you’ll check if the fly is giving you the finger.
If you’re Irish, you lift the fly out and drink the coffee…because you’re so hungover you need the coffee if you have any chance of surviving until dinner.
If you’re a gay man, you carefully dump the coffee down the garbage disposal, then get the cup steam-cleaned as per directions from the gentleman at the other end of the Villroy & Boch Emergency Hotline.
If you’re a lesbian, you grab it with your handy Leatherman pliers always located on your hip and fling it into the sink.
(FTR-- I’m as queer as a pink three-dollar bill in leather shorts.)
If you’re from Rwanda you use that as an excuse to force the neighboring villagers out of the country.
If you’re from Nepal you speculate about your cosmic relationship to the fly, decide you are brothers, then commit fratricide so you can drink in peace and quiet.
If you’re from Cuba, you use the fly to speculate about the health of the local crops.
If you’re George Lucas, you add CGI to the coffee to show the fly trying to scald and drown the coffee first.
If you’re a Doper, you Pit the fly. And the place that sold you the coffee. Then the other Dopers tell you what a wanker you are for pitting the fly. Or the place that sold you the coffee. Then Giraffe moves it to MPSIMS. Then everyone says how icky that is and tells their fly/coffee, fly/soup, hair/hamburger, walnut shell/ice cream stories. Then some people tell you how to sue the place that sold you the coffee. Then some lawyers chime in and tell you how they’re not your lawyer but you could call the local university and get a free one, and they’d sue if they were your lawyer. Then people argue with the posters who aren’t your lawyer.
Then the thread is locked for soliciting legal advice.
If you’re a Google advertising representative, you post ads for “Fly mailing lists,” “Great eBay deals on flies and coffee,” and “Wholesale gourmet fly coffee.”
If you’re black, you sue the shit out of Waffle House for racial discrimination.
If you’re a West Coast Canadian the fly is changing colours and humming. You say "Whoa, dude!*, freeze dry both the coffee and fly and smoke it.
If you’re a engineering major you try to come up with some wat to keep flies form getting into the cofee.
If you’re a chem major you try to think of a way to make the coffee in such a way that flies will stay out of it. If you’re a bio-chem major you make it so it has horrible side effects and sell only to people with perscriptions.
If you’re a film major you use it as inspiration for a film that makes comments about the greedy corporate nature of society.
If you’re in pre-med you know that drinking the fly won’t hurt you, but throw it out anyway.
If you’re in pre-law you decide to sue the cofee place to pay for the rest of education.
If you’re a physics major you assume a spherical fly, and accidentally drink it while deep in thought.
I would have said that if you’re Japanese, you videotape a girl drinking the coffee with the fly in it, then make copies for all your friends to masturbate to.
If you’re Korean, you complain that the Japanese got a bigger fly.
In Russia – Fly drinks YOU!
If you’re Rumsfeld, you decide that the fly is a Weapon of Mouth Destruction and order a surgical carpetbombing of the cafè. (Or is that café? Bugger it, those dots over the e’s are probably unamerican anyway.)
If you’re a Norwegian Conservative Prime Minister, you call Washington and ask what you should do about the fly problem.
If you’re a Norwegian Socialist Prime Minister, you hold a press conference stating that while US is a near and dear ally, we’re an independent country and will decide on our own how to deal with this situation. You then call Washington and ask what you should do about the fly problem.
If you are a New Zealander, you quickly proclaim drinking fly coffee as an extreme sport and begin marketing it to tourists.