The 40-year-old actress has slammed her former friend - who she met almost 20 years ago - for being a ''plastic'' robot with a strained vocal ability when she bumped into her a few years ago while waiting for a lesson from voice coach Eric Vetro.
Writing in her new memoir, 'Spelling It Like It Is,' Tori said: ''As I sat waiting outside his music room, I heard his prior appointment working with him in the other room.
''It was some actress singing horribly off-key ... That made me feel better. I heard him say good-bye and then the actress walked out of the room. It was Katie Holmes.
''I didn't know whether we should hug or shake hands. But the signal from her was immediately clear: Don't even come close.''
Tori attempted to put the frosty welcoming behind her by mentioning that she had children around the same age as Katie's daughter Suri, but when the brunette beauty failed to acknowledge the '90210' star's children, she got ''annoyed.''
Tori explained: ''Come on. Okay, I know you're busy. But you're in the public eye. Don't tell me you don't follow the tabloids. Don't tell me you don't know anything about other celebrities and their kids.
''Then we stood there. She was just plastic. In a perfectly polite way. ... My pits were drenched. I never sweat. It was that awkward. I thought, I know you're not a robot because you can't sing for sh*t ...''