Malaphors

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.