When she said he was "as subtle as a sledgehammer," she was using ironic simile.
a figure of speech that expresses a resemblance between things of different kinds — usually formed with "like" or "as" — as in "She is as quiet as a mouse," or "It’s like looking for a needle in a haystack."
While metaphors and similes are both techniques of figurative language. The distinction is that a simile explicitly shows that a comparison is being made, by using words such as "like" or "as". A metaphor simply substitutes words assuming the reader will understand the meaning should not be take literally. "She is like a diamond in the rough" is a simile; while "She is a diamond in the rough" is a metaphor.
When she said he was "as subtle as a sledgehammer," she was using ironic simile.
I believe this simile largely speaks the truth.
Darwin, Charles -- The Origin of Species
...the old simile of the needle in the haystack would be mild indeed compared with his brother’s chance of finding him.
London, Jack -- The Sea Wolf
It was falling so hard that it looked like white sparks (and this is a simile, too, not a metaphor).
Mark Haddon -- The Curious Incident of the Dog in the Night-time
His idea of it was that he had been making a fool of himself, running around like a chicken with its head cut off—such was the simile that occurred to him.
Jack London -- To Build a Fire
He made his mark with such economy that he was able to complete the entire circuit without having to reload once, or, to change the simile slightly, he did it all on one tank of fuel.
Farley Mowat -- Never Cry Wolf
Everyone knew about Abby’s poems, not to mention her fondness for similes.
Anne Tayler -- A Spool of Blue Thread
People were more often-he searched for a simile, found one in his work-torches, blazing away until they whiffed out.
Ray Bradbury -- Fahrenheit 451
One could not stand and watch very long without becoming philosophical, without beginning to deal in symbols and similes, and to hear the hog squeal of the universe.
Upton Sinclair -- The Jungle
The matron expressed her entire concurrence in this intelligible simile; and the beadle went on.
Charles Dickens -- Oliver Twist
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He paused, apparently taken by the unique magnificence of his similes.
Christopher Paolini -- Eldest
Colonel Korn was pleased with the simile and filed a mental reminder to repeat it the next time he found himself in General Peckem’s presence.
Joseph Heller -- Catch-22
"Weathercock can without the wind," suggested Jo, as he paused for a simile.
Louisa May Alcott -- Little Women
A good swift simile, but something currish.
William Shakespeare -- The Taming of the Shrew
These were attached to a battery of electronic equipment—imagery intensifiers, rhythmic modulators, alliterative residulators and simile dumpers—all designed to heighten the experience of the poem and make sure that not a single nuance of the poet’s thought was lost.
Douglas Adams -- The Hitchhiker’s Guide to the Galaxy
The simile conveys the hero, named after a river on whose banks he was conceived, to another river.
Homer -- The Iliad
In poetry, they must be allowed to excel all other mortals; wherein the justness of their similes, and the minuteness as well as exactness of their descriptions, are indeed inimitable.
Jonathan Swift -- Gulliver’s Travels
The simile was quite perfect, and the English turkey looked down with complete bewilderment upon the dainty little French bantam, which hovered quite threateningly around him.
Baroness Orczy -- The Scarlet Pimpernel
But the wisdom of our ancestors is in the simile; and my unhallowed hands shall not disturb it, or the Country’s done for.
Charles Dickens -- A Christmas Carol
A delicately transparent simile reveals that her defenses are beginning to dissolve: The skin of her pale face grew moist the way pure snow softens and glistens on the mountains, thawed by Southwind after powdering from the West, 20.
Homer -- The Odyssey
Now, if that simile doesn’t put you off reading entirely, you know you’re serious.
Thomas C. Foster -- How to Read Literature Like a Professor
Thorpe never finished the simile, for it could hardly have been a proper one.
Jane Austen -- Northanger Abbey
Well, out of the five or six millions which form your real capital, you have just lost nearly two millions, which must, of course, in the same degree diminish your credit and fictitious fortune; to follow out my simile, your skin has been opened by bleeding, and this if repeated three or four times will cause death—so pay attention to it, my dear Monsieur Danglars.
Alexandre Dumas -- The Count of Monte Cristo
He was but a poor man himself, said Peggotty, but as good as gold and as true as steel — those were her similes.
Charles Dickens -- David Copperfield
O, yes, into a thousand similes.
William Shakespeare -- As You Like It
What an old, old simile that is, between man and timber!
William Makepeace Thackeray -- Vanity Fair
You have a good memory, Randy, and that’s a good simile.
Pat Frank -- Alas, Babylon
It is useless to warn the reader not to take literally all the similes which we are obliged to employ here to express the singular, symmetrical, direct, almost consubstantial union of a man and an edifice.
Victor Hugo -- The Hunchback of Notre Dame
What becomes of your simile about the orchid?
Oscar Wilde -- The Picture of Dorian Gray
The liberal significance of this simile was appreciated.
Fyodor Dostoyevsky -- The Brothers Karamazov
He turned to Miro, a simile of triumph on his face, his eyes bright and flashing, his flesh flushed with youth.
Robert Cormier -- After the First Death
An altogether apt simile, Ramius thought.
Tom Clancy -- The Hunt for Red October
Even Scoresby, the justly renowned Right whaleman, after giving us a stiff full length of the Greenland whale, and three or four delicate miniatures of narwhales and porpoises, treats us to a series of classical engravings of boat hooks, chopping knives, and grapnels; and with the microscopic diligence of a Leuwenhoeck submits to the inspection of a shivering world ninety-six fac-similes of magnified Arctic snow crystals.
Herman Melville -- Moby Dick
There’s no simile for his lungs.
Charles Dickens -- Bleak House
What I saw in him—as evidently as the indestructible ramparts of Old Ticonderoga, already cited as the most appropriate simile—was the features of stubborn and ponderous endurance, which might well have amounted to obstinacy in his earlier days; of integrity, that, like most of his other endowments, lay in a somewhat heavy mass, and was just as unmalleable or unmanageable as a ton of iron ore; and of benevolence which, fiercely as he led the bayonets on at Chippewa or Fort Erie, I take…
Nathaniel Hawthorne -- The Scarlet Letter
A disobliging simile involving Mrs. Callendar occurred to his fancy.
E.M. Forster -- A Passage to India
The General was a portly, ugly man, his manners were not refined, and his talk was conspicuous for an eagerness to apply military similes to a very wide variety of matters.
Kazuo Ishiguro -- The Remains of the Day
Amory continued the simile eagerly.
F. Scott Fitzgerald -- This Side of Paradise
He had never before seen a woman’s lips and teeth which forced upon his mind with such persistent iteration the old Elizabethan simile of roses filled with snow.
Thomas Hardy -- Tess of the d’Urbervilles
The simile does not appear often, but when it does it is with good effect.
Unknown -- The Epic of Gilgamesh
All that silence and absence of goings-on is the stillness of infinite motion—the sleep of the spinning-top, to borrow the simile of a well-known writer.
Thomas Hardy -- Jude the Obscure
Philip in his happier moods indulged Tom to the top of his bent, heightening the crash and bang and fury of every fight with all the artillery of epithets and similes at his command.
George Eliot -- The Mill on the Floss
Mrs Deborah is introduced into the parish with a simile.
Henry Fielding -- Tom Jones
I can’t define it and can’t find a simile for it.
Ford Madox Ford -- The Good Soldier
In the meantime, I stepped to the card-rack took the letter, put it in my pocket, and replaced it by a fac-simile, (so far as regards externals,) which I had carefully prepared at my lodgings—imitating the D— cipher, very readily, by means of a seal formed of bread.
Edgar Allan Poe -- The Purloined Letter
All similes and allegories concerning her began and ended with birds.
Thomas Hardy -- The Return of the Native
Could there be some sort of Freudian symbolism in your choice of similes?
Stieg Larsson -- The Girl Who Played with Fire
The effect is as if the voice had been dyed black; or,—if we must use a more moderate simile,—this miserable croak, running through all the variations of the voice, is like a black silken thread, on which the crystal beads of speech are strung, and whence they take their hue.
Nathaniel Hawthorne -- The House of the Seven Gables
His celebrated passages are quoted by everybody; they are in half the books we open, and we all talk Shakespeare, use his similes, and describe with his descriptions; but this is totally distinct from giving his sense as you gave it.
Jane Austen -- Mansfield Park
A strong, sweet, fresh odour seems to rise from it, and Henrietta—pardon my simile—has something of that odour in her garments.
Henry James -- The Portrait of a Lady - Volumes 1 & 2