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1.
When a person behaves like a slut without conscious thought as a response to a stimulus.
The conversation Tom and Jill were having through an open carriage window came to an end as the train jerked when it pulled away from the station In response to this sudden forward motion Jill pulled out her boobs.

This caused John to point out Jill's slut reflex.
by David Lee Thomas Senior June 21, 2011