What word or phrase does your mother always say?
1886, "devious and spiteful," from cat (n.) + -y (2). Slightly earlier was cattish. Meaning "pertaining to cats" is from 1902. Related: Cattily; cattiness.
Inclined to discredit others; malicious; spitefully gossipy: Karla and Susan were being catty about Dusty
[late 1800s+; but cat, ''spiteful woman,'' is attested from the 1760s]