text: You invite your teenagers friend to your house as often as possible and try to be a positive influence on the friend. By having them to your house, you can tell if you really should disapprove of the friend or not. If you say something negative about the friend, you will labeled as the old person who just doesn't know how things are today. By having the friend to your house and being kind towards the friend, you will look like the good guy in the eyes of your teenager and, if the friendship lasts more than a few weeks, you will be in a much stronger position to question certain aspects of the friend that you disapprove of.