Jackie is a girl that Uncle Grandpa visited in the episode "Not Funny". She is a girl who never laughs at anything because she believes that laughing is a sign of immaturity. Uncle Grandpa tried to teach her how to laugh in the episode "Not Funny", but she did not laugh at any of his jokes. It was then revealed that she had been holding back her laughs inside of her and they were taking the forms of monsters called Laugh Gremlins. Eventually, she held back so many laughs, she exploded and all of the laugh gremlins came out and terrorized the city. Jackie defeated them by laughing at Uncle Grandpa's jokes and then changed her personality from a humorless girl, to a hilarious girl with the nickname of "Whackie Jackie". She is voiced by Jackie Buscarino.
Jackie is a short girl with short brown hair and a yellow hairband and freckles. She wears a yellow shirt with a black tie and a green skirt. She also wears black shoes and white socks.
Jackie used to be an unhappy girl who never laughed at anything because she felt she was too mature for that. It was revealed however, that she actually does take humor from funny jokes and she just contains her emotions. Her new personality, is the opposite of what she was before. She is now way more open about her hilarious personality and she is always ready to make jokes and have fun.