Watch the video for the overview:
Step 1: Supplies
1. 35mm canister
They will give you these for free at Walgreens or most one hour film development labs.
The white ones with the tighter lids work better than the black ones.
2. Can of compressed air
Your common air duster - found at most offices. Used for blowing the dust out of computers and keybaords.
3. Some confetti
I bought some for a dollar to make it stand out more in the video, but those holes from the hole punch work great!
Step 2: Fill the canister
WARNING The liquid inside is extremely cold and extremely flammable. Caution is advised, especially when dealing with something that can both cause frostbite and severe burns.
Once the liquid is inside, quickly dump as much confetti inside as you can, without getting any in the way of the lid. (If the lid cannot close tightly, the pressure will not be able to build.)
Finally, close the lid tightly, set it next to your intended victim and then quickly walk away!
Step 3: Kaboom!
It will take anywhere from 5 seconds to a good minute to explode, depending on several factors.
If you spray a lot of liquid inside, it will take longer to evaporate and build up pressure.
If the ambient air temperature is high, the liquid inside will likely evaporate much faster.
For a bigger boom, turn the canister upside down and use more liquid. Stand clear of it if you do. The resulting explosion is pretty violent, especially for a little canister.
Watch the video again to see what I mean. I filmed that in my garage, where the ceiling is about 15 feet high. Listen to how fast the canister bounced off the ceiling and then the floor again.