I am an electrical engineer and comments like this should be removed because it is complete nonsense.
The common wire is/should be Zero volts, In my country the Electricity provider will connect the common wire to the earth/grounding wire when it enters the meter, they to this to equalise it with the ground, the common wire is also connected at the power plant and or distribution stations.
Only the live wire has a voltage in normal cases, yes, if you cut the common wire and touch the one coming from the load it will have the same voltage as the live wire, but this is then faulty.
The 110/240 volts AC means Amplitude Current and what the live wire does is it goes +110V/240V positive against the common wire and the same negative.
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Now, for those having the issue the OP started this thread with, it is "normal" to feel this depending on how well the 0 Volts common wire is Zero, if your common wire is connected to the grounding as in my country you will feel nothing or very little.
It also depends on if you wear shoes, bare feet and what surface you stand on,if it's bare feet on a tile floor you will feel it more, lift your feet from the ground if you are sitting and it's gone.
NO need to bring it to Apple, it's not their fault, well sort of, if they make them of plastic the issue wouldn't be there, it's your wiring.
You shouldn't be afraid though, it's a minor annoyance, nothing more and it won't kill you.