A callous Porsche driver struck a 14-year-old boy on a Brooklyn sidewalk Sunday night, then screamed at another driver involved in the crash instead of helping the teen as he moaned in pain, according to a witness. The scene, which unfolded just after 6 p.m., was one of two crashes in the city that left pedestrians badly hurt Sunday night, officials said. The unsuspecting teen was absorbed in a video game on the corner of Manhattan and Greenpoint Aves. in Greenpoint when the Porsche struck him, said witness Eryk Kobuk, 20. The Porsche’s driver, Guo Lu, 39, was arrested at the scene and charged with reckless endangerment, police said. The boy, whose identity wasn’t available Sunday, was taken to Bellevue Hospital in serious condition. He was expected to survive his injuries, cops said. Kobuk said he heard a driver blasting a car horn. “There was a white Honda Accord coming out of a parking space on the street and the white Porsche was stuck behind him,” Kobuk said. The Porsche driver “got road rage” and tried to maneuver past, but the Accord struck his sports car in the process, Kobuk said. “And then the driver of the Porsche hit the gas and lost control and he drove onto the sidewalk,” Kobuk said. “When the Porsche hit the kid, the kid went flying 10 feet like a little rag doll. His body hit the sidewalk so hard.” Kobuk said he rushed to the boy, who was groaning and barely conscious.