Green’s Dictionary of Slang

shithouse rat n.

1. used as a general negative image.

[UK]T. Lewis GBH 74: ‘Of course Farlow’s stupd. But [...] even shithouse rats can see in the dark’.

2. used in comparatives as a (usu. negative) measure.

In phrases

crazy as a shithouse rat (adj.) (also crazy as an outhouse rat, ...a rat in a shithouse, ...a shit-eating rat)

(US) extremely unstable; thus used attrib (see cite 2023).

[US]S. King Stand (1990) 728: Boy, you sound as crazy as a rat in a shithouse. That’s OK. I like crazy people.
[US](con. c.1967) J. Ferrandino Firefight 22: He’s crazy as a shit-eating rat.
[US]E. Little Another Day in Paradise 30: Alcohol [...] makes ya [...] act as crazy as a shithouse rat, crying one minute, killing people the next.
[US]C. Hiaasen Nature Girl 167: You’re as crazy as a shithouse rat.
[US]M. McBride Swollen Red Sun 207: ‘He’s crazier than a shit-house rat. Hell, he put his own mom in the hospital’.
[US]S.A. Crosby Razorblade Tears 111: ‘You really are crazier than an outhouse rat, ain’t ya?’.
[US]F. Bill Back to the Dirt 175: ‘You done went shithouse rat loco on this wannabe kingpin’.
cunning as a shithouse rat (adj.) (also cunning as a dunniken rat, ... a dunny rat, ...a rat with two tails, ... a sewer rat, cute as a shithouse rat, shifty as…)

(orig. Aus.) very cunning; sometimes euph. as …lavatory rat.

[Aus]Truth (Sydney) 12 May 5/4: In concocting a deliberate crime, she was [...] as a cunning as a sewer rat.
[[Aus]Bulletin (Sydney) 12 Jan. 14/3: He’s my ruddy off-side leader, / And a skulking swine at that – / He’s as lazy as an M.L.C., / And as cunning as a rat].
[Aus] X. Herbert Capricornia (1939) 445: They’re as cunning as dunnikan rats.
[Ire](con. 1940s) B. Behan Borstal Boy 189: That fellow’s as cute as a shit-house rat.
[UK]C. Rohan Delinquents 136: Mrs. Hansen called Lola [...] cunning as a shit-house rat.
[Aus]F.J. Hardy in Great Aus. Lover Stories 121: Cunning as a lavatory rat.
[Aus]R. Fitzgerald Pushed from the Wings (1989) 66: Boss’ll have something up his sleeve. He’s as cunning as a shithouse rat.
[Aus]M.B. ‘Chopper’ Read Chopper From The Inside 28: He is as mad as a hatter, as shifty as a shithouse rat, smart as a whip and as dangerous as a black snake on a dark night.
Butler & Angelo Aus. Phrasebk 33: As cunning as a dunny rat.
[Aus]P. Doyle (con. late 1950s) Amaze Your Friends (2019) 199: Max gave me his shithouse-rat smile.
[UK]Guardian 5 Sept. 35/2: Specific to New Zealand (you don’t want to be a sexo or kid fucker in parrie Max, unless you’re cunning as a shithouse rat.
[Aus]Bug (Aus.) July 🌐 But, Bash, you gotta understand you don’t get to be boss cocky of any tinpot Aussie outpost dunny unless you are as cunning as a shithouse rat.
letter to Guardian (NSW) at www.cpa.org.au 🌐 He shows signs of being as ‘cunning as a shithouse rat’. What a contribution he makes.
[NZ]K. Hulme Bone People 211: Simon has the luck of a proverbial dunny rat.
[Aus]M. Glorie Bookshop on Jacaranda Street 368: I’ll lay a bet he's told you he’s dying of a broken heart. Told me the same bull and I fell for it big time. Our Jim’s as cunning as a dunny rat.
[Aus]T. Spicer Good Girl Stripped Bare 231: Our son — who’s as cunning as a rat with two tails.
grin like a shithouse rat (v.)

to look pleased with oneself, to sneer.

[Aus]C. Hammer Opal Country 152: ‘Yeah [...]’ she says, grinning like a shit-house rat, making sure he knows she doesn’t believe him.
have eyes like a shithouse rat (v.)

to have shifty, but acute eyes.

[UK]Partridge DSUE (8th edn) 371: [...] since ca. 1910.
lucky as a shithouse rat (adj.)

(US) very fortunate.

[US]‘Iceberg Slim’ Pimp 86: Brother, you are as lucky as a shit-house rat.
ugly as a shithouse rat (adj.) (also ugly as a rat’s ding)

(Aus.) extremely unattractive.

[Aus]R. McDonald Rough Wallaby 211: He invented this character for her, where she was nine hundred years old, ugly as a rat’s ding.
[Aus]G. Seal Lingo 78: There is also the crass but widely used shithouse, a term which has generated many useful and colourful combinations as ugly as a shithouse rat, built like a brick shithouse.