Thanks to Bill Hader, Grace Aroune is officially the coolest kid in school. As part of her Make-A-Wish Foundation gift request, Aroune asked the Saturday Night Live alum to visit her Elma, N.Y., high school to prank her senior class, and as the actor told HuffPost Live, the results were nothing short of hilarious.

Orchestrating her senior prank with just the school's principal, Dennis Kenney, being kept in the loop, Aroune invited Hader to pose as a visiting fireman who needed student participation in a fire safety video. "I was an old firefighter who went from classroom to classroom giving really bad advice and making the kids do weird drills like stop, drop, and roll," Hader told HuffPost Live of the stunt during an interview on June 15.

Hader, who'll soon appear in Pixar's Inside Out, said he even poked fun at the unassuming teachers during his June 11 prank. "I'd argue with the teachers, because they didn't know who I was," the comedian said. "They asked why there weren't more fire extinguishers in schools, and I went 'money!'"

As the joke became more elaborate, one student finally recognized him. "We did four classes, and by the end, a girl did the Stefon face to me, so they figured it out," he said, referring to the flamboyant SNL character he's best known for. Later, Hader used his street cred to his advantage to reveal the rouse. "Grace had me do Stefon over the loudspeaker," said Hader, who surprised students during an assembly and stuck around to sign yearbooks and give autographs.

Summed up the comic: "It was so fun!"

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