Here's what you do. Go down town, and buy some schwag. Then, take it over to his house. Wait 'til he loads it up without asking, and takes a hit and go, "Oh, shit, bro! You just took the fattest hit of sherm I've ever seen anyone take!" Proceed to laugh as he thinks he's "tripping" on PCP. Make sure to add things like, "You don't look so good, man?" "Haha, your lips are blue." He won't ever smoke any of your weed again.