Hyperforeignism is the mispronunciation of words borrowed from foreign languages…but it’s actually a sort of an over-pronunciation, so correct that it’s circled back around to incorrect again.
The noun octopus is often made plural in English as octopi, originally from the mistaken belief that all Latin nouns ending in -us take -i to form their plural. However, this is only correct for Latin masculine nouns of the second declension. For Latin fourth-declension nouns, such as manus, the singular and plural forms both end in -us. For third declension nouns such as octopus, the plural is less regular. The noun octopus in Latin is a third-declension noun borrowed from the Greek. Although octopuses is generally considered correct in modern English, its plural in Latin is actually octopodes.
An easier example of this is prix fixe. The common mispronunciation is something like “pricks ficks” but the hyperforeign version is “pree fee”, which is how one might presume the French would pronounce it. The correct pronunciation is actually “pree ficks”. See also gyros. (via clusterflock)