"I was expecting to not like him very much when I first met him," Rogen, 32, told PEOPLE with a laugh at the movie's premiere Monday in Los Angeles. "The first time I met him I assumed he'd be a little f–er, but that was eight years ago."
Rogen adds: "I was proven very wrong because he's a sweet, nice guy … He was just so nice, cool and very self-aware and self-effacing and endearing, and all those things that make someone hard to hate."
For Efron, 26, it was important to get Rogen to come around.
"I really made some extra effort, and after a while I think I wore him down a bit," he says. "I've respected Seth since the first movie that I saw him in. He rebranded comedy, and I identified with it, every single part of it: mind, body and spirit. That's how I want to be."
On the topic of unruly neighbors, PEOPLE asked both actors about their living situations right now – and it turns out they're polar opposites there as well.
"My current neighbor is a real a–hole," says Rogen. "He's been building his house for 20 months. Every morning at 7:30 a.m. he starts, and I hate him."
Efron has been having better luck. "I have great neighbors," he says. And in fact, in the past he's been the one annoying his neighbors.
Asked for details, he replied with a laugh: "Too many things to talk about right now. Standard stuff that comes with being 22 and having a house."