The name for a deviant sexual act where a male third party intrudes on a heterosexual couple's act, then forces anal sex with the female partner. The third party is usually a friend of the initial male partner.
Actual message board topic:
Subject: "Can you be charged with rape for doing the sneak king? (suprise butt sex)?"
Body: "You bring a girl back to your place and start having sex with her on top. Then when she is really getting into it your buddy, who she doesn't know about, comes out of hiding and sticks up her anus and says sneak king *****"