Go for a classic: get around 7 meters of razor wire, a shitload of super glue, and a 3+ story building. Climb on top of the building and secure the razor wire to something. Tie a slipknot or noose it the razor wire around your neck. Next, dip your hands indie super glue and fixate them to the sides of your head. Once the glue is dry, jump off onto something that would cushion your landing (such as a dumpster or a tourist from Burgerland). If done successfully, when you jump your head should be cut off by the razor wire, and when you land it'll appear as if you ripped off your own head. Bonus points if you make a weird face when you die.
