So earlier in the thread, I talked about misused phrases like "doggy-dog world." It turns out there's a name for that kind of thing. It's called an eggcorn. I don't know why, but my guess is that it comes from somebody mishearing the word "acorn," and calling it an eggcorn. "Mondegreen" is another word for the same thing, but it's used primarily for misheard lyrics in a song or poem now, with "eggcorn" being the word for conversation.

This looks like a fun site. The Eggcorn Database