Useful tip: carry a metal object (keys, soda can) with you. Grab it with as much surface area as possible (holding the twisting part of the key, or the whole of the can) and use the tip of the key or lid of the can to touch metal. Because you've spread out your contact over a much larger area, you won't feel the shock. You can use this to get some really impressive sparks - I've gotten as much as 5-6 mm long.