[1891+ Army; perhaps fr an early 1800s sense, ''unbroken Army mule''; perhaps also fr the fact that a newly commissioned officer might have shoulder straps made with material cut off the shirt-tail]
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 all shook up
all shook up
Greatly disturbed or upset, as in His letter left her all shook up. This slangy idiom uses shook instead of the grammatically correct “shaken” (for “agitated”) and adds all for emphasis.
[ Second half of 1900s