Someone who's puckish is up to a little trouble. Your puckish friend might play practical jokes on you, but they're more silly than mean spirited.
You can imagine a puckish person with a naughty twinkle in her eye. She might drive you crazy, but she also makes you laugh. This impish adjective dates from the 1860s, and we have Shakespeare to thank for it. It comes from Puck, the mischievous fairy-like creature from English folklore, made famous after being a character in Shakespeare's "A Midsummer Night's Dream."