Sassy means "bold or fresh." If you see your teacher in the grocery store with her attractive, well-dressed husband and you charge right over to say, "Who's the hunk?" that's being very sassy.

Sassy comes from saucy, as in: bold, spicy, and impertinent. It's fun to be sassy when talking with friends, but when you start saying things to teachers, bosses, and other people's parents that would embarrass a more timid or manners-minded person, you probably have crossed the line from sassy to inappropriate. The same goes for sassy dressers — you have to know when to leave the neon heels at home.

Definitions of sassy

adj improperly forward or bold

fresh, impertinent, impudent, overbold, saucy, smart, wise
used of temperament or behavior; lacking restraint or modesty