A big difference between figures of speech and improper nouns is that the first are almost universal. Moreover, getting a figure of speach 'wrong' will generall

A big difference between figures of speech and improper nouns is that the first are almost universal. Moreover, getting a figure of speach 'wrong' will generally cause quick reaction. Hence they are easy to learn, and there is a self-correcting mechanism. Meanwhile an improper noun can evade detection by those not in the know, and there is no self-correcting mechanism of wide public consciousness to teach those who are not in the know.