The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with knock into a cocked hat
knock into a cocked hat
Debunk, render useless or unbelievable. For example, His findings knocked our theory into a cocked hat. This expression alludes to a style of hat with the brim turned up on three sides—the three-cornered (tricorne) hat worn by officers in the American Revolution—giving it a distorted look.
[ Early 1800s