Not even one!

Simply put, do not SMOKE!!

This was reported many places, but I will show you Forbes' version:

THURSDAY, May 25 (HealthDay News) -- Children who light up just once are twice as likely to become steady smokers later.

British researchers report that, among 11-year-olds, the desire to smoke can lie dormant for more than three years after trying just one cigarette.

The researchers call this a "sleeper effect," and it doubles the risk that a child who smokes just one cigarette will become a regular smoker, according to their report in the July issue of Tobacco Control.