The Portable Pneumatic Variable Payload Delivery Device is made of cheap materials (PVC pipe, a lot of tape, etc.) and is great for close-range goo blasting. The truly trigger-happy can even fill a cartridge with flour to make cleanup virtually impossible.
Now, this device might seem a little conspicuous for a town hall meeting, but any angry mob will tell you that nothing stimulates productive political discourse like a little burning molasses to the face. [PenfoldPlant’s Instructables via Dvice]