For those of you not familiar with the film, Marty (Michael J. Fox) is high school student in 1985.  With the help of a time-traveling car, he is transported back on time to 1955, where he gets to spend time with his teenage parents. 

Before Marty travels back in time, there is a scene in which we learn that his mother, Lorraine (Lea Thompson), has a very obvious drinking problem.  Consider that fact as you watch the following clip in which Marty shares a drink with his teenage mother in 1955:

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I find this interesting because Marty is clearly acting like the adult in this scene.  Even Lorraine acknowledges this when she says to Marty, 'You're beginning to sound just like my mother.'  The reason that Marty sounds like the adult is clear:  Marty has seen the future.  He knows what years of drinking and smoking can do to a person.  He has seen the toll it has taken on his own mother.

Sadly, it is this lack of knowledge and experience that leads many teenagers to choose addictive chemicals such as tobacco and alcohol.  Teenagers have a sense of immortality that blinds them to the long-term consequences of these addictive substances.  Sadder still is that films perpetuate the myth that tobacco use is cool... that it is the perfect act of defiance as teenagers struggle for independence.  By the time teenagers realize that they have ben led down a path of false promises, many will have become addicted to tobacco and unable to overcome that addiction."