Seth Rogen has no problem telling people how sexy he thinks his 'Neighbors' co-star Zac Efron is. Rogen was on 'Conan' promoting 'Neighbors' when he declared Efron to be "The sexiest motherf---r alive."

"The first time I saw him with no shirt on, I thought there was something wrong with him, honestly," Rogen joked. "He has so many bumps sticking out of his body. My body is like one big bump, and his is like 87 different little bumps that come together."

Rogen added, "In the movie I make a joke, it's like his whole body is like a giant arrow that points to his d---." He also revealed that Efron kept working out in between takes while shooting, which had them changing the script to show him off shirtless multiple times.

"We had to keep writing into the scenes that I would touch his body, because I would look at it and just want to reach out and touch it, as though it was a mirage of some sort."

'Neighbors' is a comedy co-produced by Rogen and stars Rogen and Rose Byrne as a couple who finds their quiet neighborhood disrupted by a loud and obnoxious fraternity next door. The couple wages war against the fraternity (led by Efron) to see who will be the first to move out.