James Franco as Laird Mayhew, an eccentric, foul - mouthed CEO of a video game company and Stephanie 's older boyfriend Bryan Cranston as Ned Fleming, Stephanie 's conservative father and Barb 's husband Zoey Deutch as Stephanie Fleming, Laird 's girlfriend, Ned and Barb 's daughter, and Scotty 's older sister Megan Mullally as Barb Fleming, Ned 's wife and Stephanie 's mother Cedric the Entertainer as Lou Dunne, Ned 's best friend and business partner Griffin Gluck as Scotty Fleming, Stephanie 's 15 - year old younger brother and Ned and Barb 's son Keegan - Michael Key as Gustav, Laird 's best friend, butler, calmer assistant and trainer, the billionaire 's European - hailing estate manager Kaley Cuoco as the voice of Justine, Laird 's in - home artificial intelligence Zack Pearlman as Kevin Dingle, Ned 's I.T. guy Jee Young Han as Marnie Dingle, Kevin 's wife Jacob Kemp as Randy the Intern Grace Ly Ngo Hazelett and Sadie Kate Ngo Hazelett as Vanessa Dingle, Kevin 's daughter Casey Wilson as Missy Pederman, the first creator of an online invitation company called StampFree Invites. Andrew Rannells as Blaine Pederman, the second creator of an online invitation company called StampFree Invites. Adam DeVine as Tyson Modell, the creator of the wildly popular Ghostchat app. Tangie Ambrose as Patty Dunne, Lou 's wife and Barb 's friend Steve Bannos as Tree Lot Owner Burt
who does the voice of justine in why him
Kaley Cuoco