No one is a complete waste of life at 17. Kids will be kids and just because he parties now doesn't mean he'll be wothless forever. But, he's a minor and your mom should take control of the situation.
Solution: steal his weed and smoke it in front of him.
2013 Audi A4 - Premium+/Sport/MMI/B+O Audio
2007 BMW E90 335i (retired)