Stefon took a break from promoting New York City's hottest nightclubs to teach some high schoolers the importance of fire prevention.

Former Saturday Night Live star Bill Hader agreed to participate in a Make-A-Wish request from Grace Aroune, a teenage girl in Elma, N.Y., that involved pranking her entire high school.

"Her wish was for me to come to her high school and pull a prank," Hader explained on Jimmy Kimmel Live. "She said, 'I want you to be a firefighter and go to each classroom and make people do weird drills and give them all this fake information and stuff, and be a weird guy'."

Watch Bill Hader return as Stefon on SNL

"I wanted something that was really memorable, like a living experience," said Aroune, who had thyroid cancer. "But also I wanted my friends and my family and everyone who's been supportive of me to also be able to enjoy it."

To pull it off, Hader dressed up as a grizzled firefighter named Mike and went classroom-to-classroom giving dubious tips on fire safety — like standing up and waving your arms around when you notice smoke.

"It doesn't add to the fire at all?" asks one kid. "THIS SAVES LIVES!" Hader bellows.

Hader also did an all-school assembly presentation where he instructed students on what to do if they see a firefighter faint: "You run. You run. Don't worry about the firefighter. He's probably already gone."

Make-A-Wish posted the entire video on YouTube:

And here's Bill Hader talking about his experience (including the nasty cold he got from shaking hands with high schoolers, aka "Outbreak monkeys") on Jimmy Kimmel Live: