Either widely accepted stories that are passed on as factual, while being nothing of the sort, or better still, stories where the facts as generally reported are true, but still are used in a misleading manner or to support false conclusions.
For the first variety there's the claim that the doctor who pioneered blood transfusions died because the closest hospital was white only and wouldn't take him. The truth is quite the contrary: Dr. Charles R. Drew, while a pioneer in the administrative work necessary for blood banking did not invent nor pioneer the transfusion process itself; and while he did die after an automobile accident in North Carolina the survivors of the wreck all claim that they got prompt and excellent care.
For the second variety a lot of people who get tired of being told to run for their health take a sardonic pleasure in pointing out, "Jim Fixx died while running!" While I don't think this is strictly true, he died a couple hours later, after suffering a massive heart attack while running, it's close enough that I don't think that the claim is false. The implication, however, for most of the smug couch potatoes who point this out, is that running killed him. Which is about as far from the truth as you could get. Fixx had been obese, a smoker, and suffered from congenital factors that left him very vulnerable to heart failure. It can be argued that his running was a very large factor in what allowed him to live as long as he did.
Sorry, fellow couch denizens, you'll need to find a better reason to stay sessile!
Anyways, share your own favorite Tru Fax! That aren't, really!