I bought what looked like a legit iPhone charger in Turkey a few weeks ago. However, if you touched the tip of the cord while it was plugged in, it would shock the hell out of you. I guess they skimped on a ground wire? I am not an electrical engineer. Would appreciate an explanation if anyone can speculate.
EDIT: I don't use this charger anymore, just to be clear.
Chargers typically aren't grounded. The AC and output sides of the charger are electrically isolated, but it seems like that isolation isn't working in your case. It's not uncommon for enough high-frequency current to leak through to be felt, but based on the description it sounds like you've got full AC leaking through. I strongly recommend you don't use this charger, since there's a real risk of electrocution in that case. I wrote the original article, so if you send me this charger I'll tear it down, figure out what's wrong, and post a writeup (my email is on the article page).
Shocks "the hell" out of you sounds substandard, but even OEM chargers leak noticeable current. I'll get a bit of a tingle by being in the circuit of HTC Evo 4G charger - phone case - me - laptop case - T60 OEM CE charger running on 120V. And the reason I even have the grounded CE charger for the T60 is because I sent the US one to their engineering department for having way too much leakage.
I don't think the legit chargers _have_ a ground, at least around here they don't.
What it sounds like is that you have a direct connection to the mains, BUT EVEN IF YOU DON'T YOU SHOULD CEASE TO USE IT RIGHT AWAY. GETTING SHOCKED IS _NOT_ HEALTHY.
Possibly a transformerless design... regardless I would guess that the DC ground side is connected to AC neutral... (but only when it's plugged in the right way and when your outlet is wired properly), so plugging it in backwards connects DC ground (the exposed shield on a USB connector) to AC Line voltage. ZAP!
EDIT: I don't use this charger anymore, just to be clear.