1. Applying muscular pressure to the anus, resulting in the self extraction of the rectum. (both voluntary, or involuntary)
Background:
A video called "goatse" was posted on steakandcheese.com in 2002. In it was an anal gangbang in which the FEMALE throws her legs over her head, and squeezes out her rectum (as if a flower is blooming). The males proceed to fornicate with the rectum while it is extracted.
A picture called "goatse" was posted on rotten.com back in 2002. In it was a weightlifting accident in which the weightlifter's rectum exploded out of his anus while attempting a squat exercise.
"That cum-farter is so loose that he/she can goatse."
"If you attempt to squat an excessive amount of weight, you will goatse."