This is an old one but good one, I first made this when i was 12. It is so simple it can be put into anything, my first version was in a ball that I would throw at a friend who would catch it... I lost a few friends that way, and the rest don't trust me or will touch anything I make anymore.

Don't use this on any one with a heart condition or anyone who will punch you.

Parts List:

Relay 
9v battery + clip
something to put it in


The relay I use is a "Sugar Cube" size hobby relay (Switching: Single Pole Double Throw)


Circuit Diagram:
Simple isn't it.

When the coil is activated it pulls the switch open which breaks the circuit, the switch then returns to default position to activate the coil again.
Anyone touching the red points will get a nasty shock. This will wear out the relay really quickly so you might want to add a switch.
You will know its working by the sound of the relay squealing.

Don't use this around sensitive equipment. I have noticed it affects the tvs in my house.

Test on yourself first.



Building my rabbit ears of pain

1. Gather parts
 

2. Open and remove cord


3. Attached 9v clip and wire between end of coil and switch arm.

4. Attached wires to coil.

5. Finished.


6. TEST (ouch... yeah it works)

7. Find victims