Both actors dove into the roles with relish, and clearly had a great time together on-set. For Franco, meeting an actual gaming expert helped him find the right tone for his character Laird. "He was really, really smart," Franco says, "but he cursed up a storm, just interlacing all these smart, interesting things he was saying with all these curse words. And back when he first started getting attention for his designs, he'd go to these conventions dressed like a snowboarder-pimp! And I was like, 'Yeah, that's the character.' Or at least he was on the surface. As crude as Laird is, he really loves this girl. Without that, it would just be Bryan's character Ned and my character undermining each other - just a Spy vs Spy movie."

James Franco and Bryan Cranston in Why Him?James Franco and Bryan Cranston in Why Him?

Cranston was the one who insisted that he and Franco meet up beforehand to hone their rivalry. "He wanted to really work on, not the line-by-line of the script, but the structure and the characters," Franco says. "And I'm glad. Because it gave me that trust. So even though I didn't have my usual gang around [longtime collaborators Judd Apatow and Seth Rogen], I felt great with this gang."

Franco was the one who decided that Laird wouldn't be wearing a shirt when he meets his girlfriend's family for the first time. "The second job I ever did was a TV movie with Craig T Nelson," Franco laughs. "He told me about when his daughter brought home this guy, a rock star. And he shows up at the table for dinner without a shirt on. And he said to his daughter, 'Can you tell it to put a shirt on?' So I wanted to do something that'd be the biggest possible kind of red flag for Ned."

Of course, the sparring between Ned and Laird does finally erupt into a big physical fight, which both actors found hilarious to film. Cranston laughs that he was the one who pushed it to the next level. "We got into a position where there was only one move my character could make," he says. "I left a mark, I know I did. I left a mark, it will always be there, in a very, very sensitive area."

To which Franco replies, "That's right. I got Walter Whited."

Watch the trailer for Why Him?