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A period of time when the quantity of messages on a facebook inbox message, or "thread", absolutely explodes. A common sign of a threadgasm is when by the time one scrolls to the bottom of the page after it refreshes to see a new post, one is already missing at least one more post that has been written since the refresh.
Our facebook inbox had a threadgasm yesterday - 250 posts in only an hour or two! My phone was basically exploding in my pocket.
by Manhunt XXX March 27, 2011