The one-sided feud continues. Seth Rogen took another shot at pop star Justin Bieber while talking to Conan O'Brien last night. After gushing about his 'Neighbors' co-star Zac Efron's muscular physique, he also talked about how he was surprised by how nice the actor is. The two met at a party years ago, back when Zac was starring in Disney's smash hit "High School Musical."

"I remember thinking: 'Oh great, I get to hate Zac Efron now, because I'm going to meet him and he's going to suck,'" Rogen said on last night's "Conan." "And then I met him, and he was so nice and respectful." He went on to say that not all young celebrities are so polite. "Justin Bieber, for instance. He didn't expect me to hate him. Why wouldn't I? I'm a thirty-year old man." 

The 31-year old actor has had a problem with the 20-year old Biebs for months now. The issue first came to light when he tweeted "All jokes aside, Justin Bieber is a piece of s---" after the singer's DUI arrest in January. When questioned about the tweet on Bravo's "Watch What Happens Live" last month, Rogen defended himself: "In my opinion, Justin Bieber is a piece of s---. He's obnoxious and ungrateful and insincere and he puts people's lives in danger with his horrible, horrible behavior," Rogen continued. "Overall he acts like a piece of s--t."

Justin Bieber has not responded to Rogen's comments. The singer is currently facing charges in Florida of resisting arrest, DUI, and driving without a valid license. He is also being investigated by the Federal Aviation Administration for interfering with a flight crew during a Super Bowl trip back in January, facing a vandalism charge stemming from a January egg-throwing incident, and fighting an assault charge from a December incident with a limousine driver.