If actor and Alzheimer's crusader Seth Rogen were filling out an imaginary application that asked questions about his music fandom, we can safely say he would not be checking off "Belieber" on any portion of said application. The actor spoke out (again!) about Justin Bieber, calling him obnoxious, among other choice adjectives.

"In my opinion, Justin Bieber is a piece of s--t. He is obnoxious and ungrateful and un-sincere and he puts people's lives in danger," the actor said while appearing on Bravo's 'Watch What Happens Live' last night (March 12).

Rogen is known for playing a lovable lug with an affinity for weed in plenty of movies, which is something he and The Biebs could relate to, since The Biebs tested positive for pot after his arrest.

However, the actor has lambasted the singer for his antics before.

Rogen had tweeted that The Biebs is a piece of fecal matter in a tweet issued after his arrest. That digital transmission received more than 200,000 RTs and was favorited nearly 170,000 times.

This interview (and situation) has all the makings of a classic Hollywood feud. Perhaps The Biebs will issue his retort in the social media space. Or he can challenge Rogen to a celeb boxing match. That would be fun!

We're certain that Beliebers, a truly loyal bunch that defends its hero at all costs, will take aim at Rogen for his comments and possibly boycott 'Neighbors,' his new film with an often-shirtless Zac Efron.

Watch Seth explain his tweet in the video above!