Instead of using flames and jet propulsion, as jetpacks are known to do, Raymond Li's invention uses water to fling you up into the air. His patent hasn't (as far as we know) been constructed yet. But it looks dangerous.
The patent says that instead of using risky propellers, rotor blades, and rocket exhaust systems that have to be attached to your back, it uses a water system only with non-flammable fluids (water) to create "sufficient thrust" for yourself. How high this thing can go, and whether it can actually work, are questions for a man actually willing to strap this on and test it himself. It's too bad whatever balls this person might or might not have had would be shot off by the high pressured water stream. [Free Patents Online via Wired]