The key to it is shock. You have to do something that will shock the kid with facing real life. And do it - don't just threaten to. If the kid won't do his school work, tell him he has to either get a job or move out, and kick him out if he doesn't get a job. Remind him he is 18, and you have no obligation to support him anymore and you are not going to support a lump. It's tough love time.