These figures are the stuff/staff of life, and I love 'em. But it is hard to keep them fresh: they soon degenerate into cliches. I refuse, for instance, to be "as happy as a sandboy" or "talk the hind leg off a donkey". I don't mind being "as happy as an eight-day corner cupboard" or "to bore the balls off a buffalo", because at least it makes you stop and think for a moment.
A colleague of mine of many years, now a lay preacher in his retirement, gave me a memorable comment on an attractive woman: "She would make a bishop kick a hole in a stained-glass window." Sadly, I never met the lady in question.
Liverpool, where I gained part of my education and a wife, is a place rich in memorable figures of speech. It doesn't take any imagination to recognise a woman "with a gob on her like a robber's dog". Nor a woman who would "eat the face off you".
The other elements in a memorable metaphor/simile are the twin devices of assonance and alliteration. For example the repeated b in the buffalo example, or the repeated o in the robber's dog example.
And rhythm. Rhythm is much harder to define, but if you say the stained-glass window example out loud, you will know what I mean, a delicious mix of spondees and dactyls, or whatever those da-da and da-de-de combinations are called. Remember scansion? Me neither, but it makes a powerful point. Take the expression "I wouldn't piss in his ear if his brain was on fire". Vivid imaginary, true, but if it didn't scan, it wouldn't work.
There are two expressions I know to describe something rare: "As rare as hen's teeth" and "As rare as rocking-horse shit". Leaving aside delicacy or social acceptability, the latter has much better rhythm. De da de da da as against De dah de da-de da da. Which is meaningless in print, but makes sense the moment you utter the two phrases.
Well, that's it for now. I hope you are not a buffalo........