I will choose excessive drinking as the youth behaviour. The question is personal, so you should answer about yourself, but I can give you some general information:
social influence:
After alcohol, you might be more impulsive and as a result loose friends. Alcohol can also prohibit the building of social bounds generally.
economic
drinking not only costs money, but drunk behaviour can lead to a destruction of personal objects, such as cars, and objects that the whole society uses such as roads,
physical
alcohol is bad for your health, and also a general negative influence on the public health
mental
Alcohol is addictive - so the person drinking will suffer from an addiction. Their family and social circle can suffer as victims of abuse of the drinker or because they are worried about the person who drinks
