Dumb Money, the breezy new movie about the GameStop stock hysteria of early 2021, starts in a hedge fund guy’s pandemic retreat mansion. Investor Gabe Plotkin (Seth Rogen) is trying to get a house demolished so he can put a tennis court there (true story, by the way) when he gets a call informing him a bunch of Redditors have blown an enormous hole in his short position against the video game retailer’s stock. A distressed Plotkin sprints through various well-manicured beachfront backyards to get to his desk in another mansion and make a call. He’s down billions, he is...