So when the two were cast to play human grandparents in the upcoming animated movie Hotel Transylvania 2, they spent the gig cracking each other up.
Offerman, 44, who plays Grandpa Mike, says that Mullally, 56, who plays Grandma Linda, was able to make him laugh with even the simplest lines. And even though the couple didn’t record together due to work schedules, he found himself laughing at her jokes.
“Like all things she touches, she has such a golden talent in animation,” Offerman tells PEOPLE in the newest issue, out June 19. “And the most mundane line like, ‘Can I get you a wash cloth?’ just cracked me up. She is somehow able to make every single line really funny.”
Offerman, who starred in the Lego Movie, says getting into character for this film was easier than expected.
“My character is pretty realistic compared to [other projects] like the Lego Movie, where I’m playing a robot pirate, so I do often close my eyes just to sort of envision the scene that I’m in.”
Offerman and Mullally’s costars in the sequel to the 2012 hit include Adam Sandler, Selena Gomez, Andy Samberg and Kevin James.
Offerman, who doesn’t have any children, says if he were a grandfather he would be a healthy mix of “tough love” and playing the good guy.
“I would probably have them out in the garden and have them out in my woodshop and be teaching them the fundamentals of being a good citizen,” he says.
“Being able to sweep the floors properly, rake a yard and shovel a snowy sidewalk. That’s tough love but then at the same time, since you’re not the parent, as soon as they fall down you’re immediately coddling them. You get to spoil them and sneak them a candy bar.”
Offerman and Mullally, who met in 2000 while working on a play together, have been married since 2003.
He says there’s no friendly competition, in terms of who’s funnier.
“Sadly that was decided many years ago when Megan [and I worked together],” he says. “It was clear who would be the master and who would be the student. It’s made for a very happy relationship.”
The movie opens Sept. 25.
For more on Hotel Transylvania, pick up the newest issue of People, on newsstands Friday