Actress Marg Helgenberger apparently wasn't a big fan of Justin Bieber when he guest starred on her hit CBS series 'CSI.'

In a radio interview in France (via RadarOnline), Helgenberger let it slip that Bieber "was kind of a brat. He was very nice to me. But he locked one of the producers in a closet and he put his fist through a cake that was on the cast's table."

As for Bieber's acting skills, Helgenberger had this to say: "Justin Bieber wasn’t 'bad' bad ... But he'd never acted before ... He's better than you'd think."

Ouch.

[PopCrush]