What it means
Saucy is cheeky with a flirty little sting to it. You use it for someone being bold, a bit fresh, maybe lightly rude, but in a way that lands playful instead of nasty. It can mean teasing, suggestive, mildly risqué, or just confidently impudent with a wink in its pocket.
Usage examples
"The seaside shop still sells those saucy old postcards full of cheeky jokes."
"She shot him a saucy grin and told him to behave himself."
"She gave a saucy little wink and slipped the extra biscuit into her bag."
"That's a saucy reply to send your boss on a Monday morning."
"Don't get saucy with me just because you've had two pints and a sudden burst of confidence."
Where it comes from
Saucy comes from sauce, which in older English could mean insolence or impertinence as well as the literal stuff you pour on food. That sense goes back centuries, and by the 1800s saucy was firmly doing double duty for cheeky, boldly rude, and a bit sexually playful too.