Language Log has been quite prolific in introducing terms for speech oddities, including the eggcorn and the snowclone. The former, in particular, came about due to the fact that the phenomenon being described didn't fit into existing categories, like spoonerisms, malapropisms, or mondegreens.
But here's one I haven't seen a label for.
We're all familiar with the template (perhaps not quite a snowclone) "it's not X", where X is meant to be something difficult. "It's not rocket science" gets about 20k Google hits. "It's not brain surgery" gets about 3.5k. Just for kicks, I also tried "it's not nuclear physics", which gets only 63 hits, so it's not in common usage. The first two seem to be accepted idioms, though, as SC has both heard them used, and has documented here that there are plenty of instances of their use on the Web. This brings us to a case where they get blended:
I don't have a name for this. I can't think of another example like it. Reader submissions are highly encouraged (both for names and examples).