Green’s Dictionary of Slang

cat’s ass n.1

[SE cat + ass n. (2)]
(US/Can.)

1. (also rat’s ass) anything exceptional or superlative.

[US]C. Bukowski Notes of a Dirty Old Man (1973) 33: jesus christ, it’s a catsass sitting there.
[US]C. Loken Come Monday Morning 36: Well, if that ain’t the cat’s ass ...! Russ Simpson, Jr., posted!
[UK]D. Gram Foxes (1980) 174: If I tell her I love her, she keeps saying I must be high ... isn’t that the rat’s ass.
[US]A. Maupin More Tales of the City (1984) 230: I walked [...] Ain’t that the cat’s ass?
[US]MTU Ridge Roamers 🌐 Brian is also sporting a polypropylene shirt. Polypro is the cat’s ass for long underwear. It wicks moisture quickly and insulates even when wet (like fleece).

2. a superior person or someone who poses as such.

[US] in DARE.
[US]B. Gutcheon New Girls (1982) 54: My dear, she thinks I’m the cat’s ass. Which I am, of course.
[Can]M. Atwood Cat’s Eye (1989) 258: We thought we were the cat’s ass. I see kids that age now and I think: brats!
W. Magnuson Eng. Idioms 🌐 the cat’s ass the best, number one, the bee’s knees. Since Val won the beauty contest, she thinks she’s the cat’s ass!

In phrases

give a cat’s ass (v.)

(US) to care about someone or something; usu. in negative.

G.A. Edwards Bureau-Rats 🌐 Do you think I asked you to come here today because I give a cat’s ass about your mind?

In exclamations

in a cat’s ass!

an excl. of dismissal or disbelief.

(con. WWII) Camerer Damned Wear Wings 220: ‘You mean you’re not going after Ploesti? Just once more?’ ‘In a cat’s ass.’.