NOTICE: I am not suggesting anyone do this! In fact, I would discourage it.
When I was in school there were 5 of us in one big house, thus lots of "stuff" happened. "plastic soda bottle bombs" were one our favorites. We made them from lots of rapidly expanding stuff. I did not take long for the neighbors to call the sheriff and they paid a visit, cited each of us for disturbing the peace. But, the "threats" they made if they had to return were not pleasant.
Notes:
* Doing this in a garage will likely lead to replacement of windows.
* 5lbs. coffee cans will do a lot of damage to a car upon return to earth.
* The neighbor with the aggressive dog will not find this funny.(even if he is in your yard)
* If it does not explode in a few minutes, it will when you pick it up.(newtons law or something)
* Placing it in the refrigerator for later use will not endear you to fellow roommates.
Also, if you think this is something, you should see a 55 Gallon barrel implode. :kickass: