Sassiness can be an off-shoot of the word, sauciness, which means: impudence, pertness; lack of shame; rude; boldness sassy also means stylish, chic and lively.
"Sassy" is dialectical for "saucy" that is impertinent, disrespectful.
"Don't give me any of your sauce," my mother used to say, if I was being impudent
to be a "diva"; to have an attitude. Sassy is an adjective that describes boldness, liveliness, spirit, and wit.