A friend of yours has been walking on the wild side for a bit too long: you might want to give them a reality check today before they start taking things too far. While it's not your job to tell other people how to live their life, you'd be shirking your responsibilities as a friend if you didn't voice your concerns: in a non-judgmental, supportive way, of course. There's no telling how they will react, but that shouldn't stop you from saying something.