It is bad to smoke if you are under 21.
Dave and Tim are students hanging out at the back of their high school when Tim offers Dave a cigarette.
Dave wants to respond to Tim's offer.
Dave tells Tim that he knows smoking is bad for your health, so he doesn't want it.
Dave accepts Tim's cigarette and allows Tim to light it for him.
Dave continues to live a healthy and long life and does not acquire any smoking related illnesses.
Dave eventually becomes unhealthy and is diagnosed with lung cancer.