I wonder if there's a name for this phenomenon. Eggcorns aren't quite right, as they're more about mishearing a word or phrase in a way that still makes sense in context (e.g. Alzheimer's disease -> old-timers' disease). Mondegreens are about mishearing a word or phrase and substituting them for something different. Those are errors in interpreting phonic elements, but there's no misinterpretation of the words for these phrases/idioms; it's just disregarding the meaning entirely and substituting a new meaning.