holy terror - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
An exasperating individual, as in He was only five, but he was a holy terror, running wild through the house and throwing whatever he could lay his hands on. The adjective holy here is an intensifier. [Late 1800s]