You should not get an electric shock from a 5v or 12v supply.
If you are getting an electric shock (hopefully very mild) there must be a build up of static electricity to voltages that are high enough to cause damage to an Arduino.
It is also possible that due to some faulty or incorrect wiring mains voltage is able to get to your apparatus - that has the potential to kill you or your friends.
Please make you images visible here. See this Simple Image Posting Guide
...R