fit to kill - 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.
Excessively, immoderately, as in She was dressed up fit to kill. [Colloquial; mid-1800s] Also see dressed to kill.