If you can't get this resolved via the landlord/leasing agency, just do something he ultimately HATES every single time you see him. If that doesn't work, every single time you see him, punch him right in the eye extremely hard. Eventually, no matter how selfish or dense he may be, he will get the point. Even if you get in trouble, it would be funny. Not to mention you always have the weed is illegal aspect you can float above his head. If he still refuses to stop, just call the cops when he isn't around and show them his stash and tell them what's up. I'm not personally a narc, but when someone is an ass and you have tried to be nice, and it involves your health, screw em.