"I ran over to him, told him I was the biggest fan in the world," Manganiello said, recounting how he asked Reubens to accompany him to an art exhibit featuring the works of director Tim Burton -- who made his directorial debut with Pee-wee's Big Adventure in 1985.
After that, the pair became friends, and Manganiello was able to pick up on some of his mannerisms, which allowed him to nail the comic character's iconic laugh. Fallon, also a Pee-wee Herman fan and impressionist, joined in on the fun and the pair riffed with Pee-wee impressions.
But Manganiello actually has quite a few impressions in his arsenal -- including late comic icon Rodney Dangerfield and Kermit the Frog, which was shockingly pitch perfect.
He even showed off his impressive impression of friend and fellow body-builder Arnold Schwarzenegger, which put Fallon's to shame, really.
Manganiello appeared on the Tonight Show to promote his upcoming animated comedy Smurfs: The Lost Village, and the former True Blood heartthrob said he's excited to finally be part of a movie aimed at a young audience.
"All of my projects for a very long time were only seen by adults," Manganiello explained. "I do a lot of work at the Pittsburgh Children's Hospital, and I would go there, and I'd say hi to the kids… and the kids would turn and go, 'Who's he?'"
"I'd say, 'I'm a werewolf on a TV show,' and they'd go, 'You're not in Twilight,' and their mom would kind of put her hand on [their hand] and go, 'No, no, he's on Mommy's favorite werewolf show,'" he joked.
"Yeah, Mommy's seen Magic Mike 80 times," Fallon added, laughing.
"But now, they still don't know who I am, because [in Smurfs] I'm a cartoon," Manganiello joked.