Takeoff of one of those anti-smoking ads.
A shot of a guy about to light a cirarette.
V/O: Smoking damages almost every organ in your body, causing heart attacks, strokes and lung cancer.
The guy looks terrified and drops his cigarette.
Cut to the same guy drinking a schooner.
V/O: Alcohol is the leading cause of liver failure worldwide.
Guy looks scared again and puts down the beer.
Cut to the guy getting into his car.
V/O: Greenhouse gases emitted from cars will cause Global Warming and rising sea levels.
Shot of guy with scared face.
Flash of scene of tsunami taking out city. 
The guy runs out of his car.
Cut to the guy eating a sandwich.
V/O: Is that a ham sandwich you're eating? Guy looks up. Two words. Swine. Flu.
The guy screams and drops the sandwich.
V/O: Every single thing is doing you damage. Don't do anything. Ever.
Final shot of the guy standing in the middle of a room, shaking with fear.
V/O: Authorised by the Hypochondriac council, Sydney.
 Alternatively, if we want to do the whole funny voice over at the end of the ad;
Blah-blah-blah-blah-blah-blah-blah (quickly)
You know what? I think I'm going to be a rebel and speak slowly.
Another idea for taking off the smoking ads was to start off as a conventional ad, but get more and more gratuitous as the ad went on, until eventually you just get ridiculously gross, eg:
This is what happens to your brain when you smoke (Starts hacking a brain up with a meat-axe).