I found this explanation on the internet which seems to sum up what odd phrases like ‘you can’t judge a book by its cover’ mean: ‘a word or phrase used in a non-literal sense for rhetorical or vivid effect.’

We, as writers, are constantly reminded that we should not use these in our writing because most people might not understand their use.

But, being that unconventional, never to be told, type, I honestly think that it sometimes adds a degree of whimsy to the story.

I remember some years ago when I working with a Russian chap who’d not been in the country very long, and though he had a reasonable use of English, was not quite up with our figures of speech.

And made me realize when he kept asking me what they meant, just how many I used in everyday conversation.

Most of these figures of speech use descriptions that do not necessarily match the word being described, such as ‘I dance like I have two left feet’.

And that pretty much sums up how good I can dance.  But …

‘Like a bat out of hell’, not sure how this got into the vernacular, but it means to get the hell out of dodge quickly.  Hang on, that’s another saying, American, and the way Dodge city was in western American folklore, if you irritated a gunslinger, then best be on your way, fast.

Otherwise, yes, you guessed it, you were at the end of another saying, you would get a one-way ticket to boot hill.  In other words, the cemetery.

And while I’m digressing, again, Yul Brynner made a trip to boot hill very memorable in The Magnificent Seven.

Then,

‘Like a bull in a china shop’, describes a toddler let loose, not necessarily in a china shop, but I have seen it happen in reality and it wasn’t pretty

‘More front than Myers’, as my mother used to say, but in context, Myers is the Australian version of the English Selfridges or Harrods or Paris Galleries Lafayette.  It refers to the width of street frontage of the stores, and means that someone has the nerve to be so confronting

‘As mad as a hatter’, though not necessarily of the millinery kind, but, well, you can guess, it’s from Alice in Wonderland

‘As nutty as a fruitcake’, provided your fruitcake has nuts in it, we seemed to have coined the phrase nutty, or nuts for people who are a little, or a lot, eccentric

You can see, if you get the references, they are somewhat apt, and, yes, they sometimes creep into my stories.