“Incompetence is a double-edged banana”

A “double-edged sword” is sharp on both sides and can cut both ways; the term is used to mean an asset that could also turn into a liability. A “double-edged banana” is soft on all sides. “Incompetence is a double-edged banana” has been cited in print since at least 1990 and means something that is a liability, no matter how one looks at it.
 
       
Wiktionary: double-edged sword
Noun
double-edged sword (plural double-edged swords)
1. (idiomatic) A benefit that is also a liability, or that carries some significant but non-obvious cost or risk.
 
Electronic Frontier Foundation
CRIME AND PUZZLEMENT
by John Perry Barlow .(JavaScript must be enabled to view this email address)
(...)
Of course, incompetence is a double-edged banana.
(...)
John Perry Barlow .(JavaScript must be enabled to view this email address)
Friday, June 8, 1990
 
Google Books
Betting on Forever
By Billy Aronson
New York, NY: McGraw-Hill
1996
Pg. 107:
But once again, intelligence was a double-edged banana. After using these materials, the chimps left them on the beach. Then the waves swept the stuff out to sea, where it all washed together to form islands of garbage.
 
PaceAdvantage.com—Horse Racing Forum
Dick Schmidt 12-25-2006 02:24 AM
(...)
Incompetence is a double-edged banana.
 
Chicago (IL) Tribune
The acid test
April 25, 2014|By FRANK STEWART, Tribune Content Agency | Daily Bridge Club
Today’s North was Grapefruit, my club member with an acid disposition and a tongue to match. He badgers his partners unmercifully.

Against four hearts West led a club. South took the king, drew trumps and led the ace and a low diamond to his queen. West won and returned a diamond to the jack, and then East led a spade for down one.
 
“Incompetence is a double-edged banana,” Grapefruit growled.
 
Twitter
A. Leach
‏@FX_Monkey
Incompetence is a double-edged banana.
1:08 AM - 23 Oct 2014