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3.
automatic, quick and without thought
Allergies are the immune system's knee-jerk defensive responses to unknown substances.
by Light joker January 14, 2007
 
1.
A spontaneous, thoughless, predictable and stereotypical reaction to something, usually an opinion or a statement.
An entire culture of American neo-conservatives has seemed to build itself on a type of knee-jerk reaction to any kind of criticism of the Bush Administration or the loyal element of the Republican Party, even from fellow conservatives -- the kind of pseudo-patriotism discouraged by Theodore Roosevelt.
by LudwigVan November 10, 2003
 
2.
To react without thinking. To form an opinion without paying attention.
When he said he was a Republican, the college student's kneejerk reaction was to boo him.
by </time> September 14, 2003
 
4.
An orthopaedic surgeon who happens to also be an idiot, despite both the excellent training and higher than average IQ.
I'm glad that the Knee Guru replaced my knee, but he is a total knee jerk when it comes to bed-side manner.
by quills1313 January 22, 2011
 
5.
A handjob from a midget
"she was kinda short but I loved her knee jerk action!"
by L0VE (the 0 is a zero) November 02, 2009