I wrote about "conflated idioms" a couple weeks ago; some of these are what's commonly known as "mixed metaphors," while others aren't. One of my favorite metaphorical mix-ups is one that occurred between a friend of mine and his dentist. At some point during a recent visit, the dentist told him that he was "sharp as a cookie." The receptionist then gently corrected him: "It's sharp as a tack." They all laughed at that, but were sort of puzzled: where do cookies come into it? Until they remembered a similar saying: "You're one sharp cookie." Which has nothing to do with actual cookies being sharp (one also sometimes hears "one smart cookie" and "one tough cookie"), but rather comes from the fact that "cookie" is an old-timey, affectionate slang term for pretty much anybody you might feel like calling that. One commenter compared it to "toots." My friend, his dentist, and the receptionist all chalked their confusion up to the fact that it was noontime and none of them had had their lunch yet. Metphor* (for metaphor*) is a "low probability" typo on the Ballard list, with three cases in OhioLINK, and 34 in WorldCat.
(Coconut fortune cookies, from Wikimedia Commons.)