impish
Definitions
Inclined to do slightly naughty things for fun; mischievous.
Relating to or characteristic of an imp; playfully annoying.
Examples
The child had an impish grin as he hid his sister's favorite toy.
She couldn't help but laugh at his impish sense of humor during the serious meeting.
With an impish twinkle in his eye, he suggested a harmless prank to play on their friends.