These rational reasons are, by the way, many and powerful. On average, each minute of smoking reduces a person's life expectancy by a minute. Smoking is addictive. Once you get hooked it is very difficult to stop. Smoking is extremely expensive.
Smoking has effects on personal hygiene.
Cigarettes are messy and they make your hair, clothes and breath stink. These reasons make smoking look very stupid to any thinking adult. Because the teenagers who start smoking are not yet thinking adults. They are, in large part, not thinking at all. They are reacting and doing, and a reactive mind does not include rational thought.