Justin Bieber fans knock down his mother, steal his hat

justin-bieber-sydney-zap2it.jpgDo not mess with Justin Bieber's mother. Or his hat.

Crazed fans swarmed Bieber at a New Zealand airport on Wednesday (Apr. 28), knocking his mother to the ground (!)  and swiping his hat right off his head. Needless to say, the Biebster was not amused.

"Not happy that someone stole my hat and knocked down my mama," he remarked on Twitter. "Come on people."

Because of the crazed crowd, he had to cancel a meet-and-autograph session. And Bieber doesn't like to cancel meet-and-autograph sessions.