While intoxicated and engaging in the act of vagina intercourse from behind (aka "Doggiestyle"), the penis, while being forcefully moved in and out of the vagina "accidentally" slips out and is subsequently slammed into the anus of the unsuspecting partner.
Pete: Man, last night I was so wasted I accidentally gave Gina the Drunken Carpenter.
Steve: Was she pissed?
Pete: She was when she woke up.
Steve: Was she pissed?
Pete: She was when she woke up.
by Morgan Candlelight December 15, 2009