When someone is cheeky, it means that they are being a little rude or disrespectful, but usually in a way that is funny and endearing (cute).
“That is a cheeky smile…are you up to something?”
“Did you just take the last biscuit? That was a bit cheeky!”
It can also be used if you are eating, drinking or doing something that you maybe should not or that is not good for you.
“I’m just going to have a cheeky burger on the way home.”
“Are you coming to the pub tonight?”
“On a Tuesday?! Well OK, just a few cheeky drinks.”