The story
From the idea of a gray rock being an uninteresting object, introduced in 2012 in an article on the Lovefraud website written by the user Skylar.
Etymology from Wiktionary, CC BY-SA 4.0.
gray rock method
Today it means: The practice of deliberately making oneself uninteresting and unresponsive so as to defend oneself against someone who wishes to elicit certain responses, such as a narcissist or psychopath. Full definition →