What is an RPJ you ask? It's a Rocket Propelled Joint.
Okay so there's no propulsion really. You simply smoke it. Through the exhaust tube. Just don't burn your face off!
The tricky part is to create your ammunition. These are high explosive warheads you see, or should I say explosive high - a strain of pure sativa called grapefruit.
The rocket tube itself is filled with green herb but I would recommend taking it out of the launcher once the warhead is gone - easier to deal with after that. How do you create it? Well I've prepared this simple MSPAINT diagram just for you.
Warning: Cannabis is to be used by responsible adults 19+ only or 18+ in Quebec. This is not to be used as an anti-tank weapon. Inhaling burning plant matter is a health hazard. Do not point towards face. Store in a cool, dry place. Keep away from direct sunlight. Use immediately once activated.