When you smoke, are you outside, or driving down the road in your car, or something like that? Or are you just chilling in your house? Because the next time that you smoke with him, do it somewhere safe like inside. And if he starts getting paranoid, just be like "Dude, it's alright. You're safe here, ok? I'm here. Nothing bad is going to happen. You wanna watch some cartoons and each some cookies?" If he's still wigging out, just be like "Look at me" and then just break out into a smile. That's what I've always done for people when they were having bad experiences with shrooms or 'cid.

Hope that helps.