Combine malapropisms and mixed metaphors, and you've got a malaphor. It's a "mixture of two idioms, creating a sort of malaprop in metaphor form." A famous example is the song "We'll Burn That Bridge When We Get There," although that was intentional. The unintentional ones are the funniest. The site Malaphors collects incidences of these idiosyncratic idioms. Here are some examples:
She called me every name under the book
I haven’t heard hide nor hair of that guy
He wasn’t the brightest bulb in the basket
Put your best face forward
Each example has the story of who said it and where. Check out more at Malaphors. This may keep me busy for a while. -via Daily of the Day
(Image credit: Skez)