"No, the 'that' in the title 'The Skin that I Live in' is not superfluous. Yes, if left out the title would still make perfect sense. But a choice was made to leave it in, which just gives a slightly different emphasis - it is not wrong. As in any writing, there are places where the 'that' can be either kept or discarded. Either way is grammatically correct. Keeping it is, if anything, more correct, if sometimes too formal. You say, vaguely, that it is 'rhythmically superfluous', when in fact it gives the title a stronger rhythm than your alternative. And you go on about 'such simple cosmetic errors'. Perhaps you should learn something about the English language before pompously making a big deal about non-existent errors."