Confront him with some bad examples of how people end up that behave like him. Biographical evidence on video or real world examples (hard to find these days, better try YouTube).
However, note that some have the ideal of becoming a junkie. Or they don't mind committing suicide. Youth can be very extreme, so even the most extreme of examples will be useless in the face of that kind of opposition.
You tell him to get a job and find another place to live, and come back for a visit if he wants to. You might let him stay another day or two, but the idea is not to be nice, it is to cut him short and make him earn his own keep.
However, note that some have the ideal of becoming a junkie. Or they don't mind committing suicide. Youth can be very extreme, so even the most extreme of examples will be useless in the face of that kind of opposition.