Dremel (rotary tool)
Note: I understand that this isn't a real Taser, or stun gun for that matter. It puts out around 10,000 volts, but with an unreasonably low amperage; too low to harm someone. You can feel it but the pain it inflicts is minor. This project was made just for fun, and isn't meant for self defense.
here are some videos of me messing with my piezoelectric "taser"