Green’s Dictionary of Slang

cat’s ass adj.

[cat’s ass n.1 ]

(US) excellent, first-rate.

[US]Current Sl. V:1 20: Cat’s ass, adj. Good, excellent.
[US](con. 1916) G. Swarthout Tin Lizzie Troop (1978) 168: You’ve made colossal, cats’s-ass fools of yourselves and me and the cavalry!