The point about smoking and health insurance is a good one, but it addresses only a small corner of a larger problem. People do lots of unhealthy things. I'm damned if I'll pay for any of it. Therefore, the following people should be denied the health care their insurance company is contractually obligated to provide by virtue of the premiums paid:
Athletes of any kind, amateur or professional. There are dozens of common sports-related injuries, and worst of all, people who "stay fit" tend to have a somewhat prolonged retirement and old age, during which they collect far more than their share of social security and require increasingly expensive care.
People who eat meat, or fast food of any description. Hydrogenated oils, cholesterol, preservatives etc.: The list goes on. It's all purely voluntary, and it all causes health problems. It's insane to demand that vegetarians pay for the bad dietary decisions of others.
Indolent, lazy people who never exercise. Let's face it, that kind of worthless, couch potato lifestyle is well-known to be harmful to your health. Hypertension and outright heart disease (not to mention piles) are no more than what you deserve, and it's grossly unfair to ask me to foot the bill.
Sky divers, hang gliders, bungee jumpers, those who ski, and the like. HELLO?!
People who drive too fast, people who run red lights, and so on.
People who don't look both ways before crossing the street.
People who drink soda, eat candy, or chew gum. They're your teeth, you pay for the dental work. Did you ever see what Pepsi does to the paint on a car?
People who use medication of any description, and also those who don't. Either way, something bad might happen.
There, I think that's everybody.