Knee-jerk Edit Meaning

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.

2.

automatic, quick and without thought

Allergies are the immune system's knee-jerk defensive responses to unknown substances.

See reflex, gut reaction