If you don't have a pin, break off the ring pull, then snap it in half, creating a sharp point.
Using the sharp point, put a series of small holes in the can.
Now your can pipe is complete.
Put the weed over the holes, put your mouth over the can mouthpiece, light the dope, and inhale. Easy. also see PIPES
Situation 2:
you've reached your last bit for joint, and you really want to get high from. You know you won't get stoned from a joint. How??
Answer: Buy a small plastic bottle. Using a lit fag, burn 2 equal sized holes at the bottom of the bottle:
| | / \ / \ / \ | | | | | | o o \_____/Stick the roach in one end of the bottle, light the joint, and smoke it through the bottle which will fill up with smoke. Use the second hole as a carb (cover it whilst inhaling and take it off to clear the smoke).