"Current will jump out of perfectly good metal pipes to go through a human full of fats and oils. It is known, Khaleesi."

I'm being facetious, of course. If your shower has a cold water pipe involved somewhere, its made of metal and in intimate contact with the ground. Cold water pipes are such good earths its common to earth ham radio equipment to them, to get the last little extra bit of sensitivity. Lightning is never going to choose you as a current path over a cold water pipe. If lightning literally struck your shower head, it would still take the cold water path to ground. You'd likely be defeated and spattered the molten metal, though...