We equate cycling so much with health that it's easy to forget that some folks just ride to get around and some people still smoke. (Though this fella looks quite trendy, fitting the image of the fixter exactly.)
But uh, gross. Didn't cigarettes go out of style in the late 80's?
Yes, Jessie, smoking when it kills you is a much slower death.
And of course, lack of a helmet might lead to death or brain damage, IF one happens to be involved in a crash (that relatively small proportion involving some kind of cranial impact) somewhere between the relatively low speeds where a helmet is effective against superficial head injuries (the kind requiring stitches etc.) and the high speed ones caused by impacts with cars going over safe road speeds, which bike helmets are not designed to save you from.
Lack of a helmet should also be counted as a factor in cranial trauma deaths from: - falling down stairs, off ladders - slipping on an icy sidewalk (or in a shower) and hitting one's head - being hit by a car while walking across the street at that kind of intermediate speed where a helmet might otherwise prevent serious injury (i.e. the exact same kind of measure that applies with bikes) - head impacts (while wearing a seatbelt) inside an automobile during a crash due to impact either with loose objects in the car or with some other surface in a car ...
If you want to tell people that helmets should be worn for protection while biking, the same applies in these other cases, which are statistically no less important, if not more. (You can google up the stats with not too too much work and time.)