A tilly
A Tilly is wild, crazy, and will do anything just to make you laugh. She looks cute but don't let that fool you, she'll pull the biggest pranks and say the dirtiest things.
Tilly: I put glitter in your lunch. I'm your friend, what did you expect?
Tilly: I told your crush you like him. You're welcome.
Tilly: I drew a mustache on your face during class. It was a masterpiece.