Okay, a weed milkshake is probably not what you expect. First things first, you must be able to shotgun a joint. To shotgun a joint you put the cherry part in your mouth and blow, out will come a stream of smoke. Take a frozen glass and hold it upside down, shotgun a joint into it until it's full of smoke. Turn glass over. B/c it's frozen, the smoke will stay in the glass. Tip back and enjoy. It's a pretty neat trick and will fuck you up too. Also, it's pretty cool under blacklight.
So there you go, a weed milkshake.