dirty straddle
When a male is taking a shit, the female climbs on and rides his dick. While riding his dick she also shits between his legs straight into the toilet. Thus resulting in a dirty straddle.
Guy: "I have to shit and I'm horny."
Girl: "Me too."
Guy: "Want to dirty straddle?"
Girl: "Hell yeah!"
Girl: "Me too."
Guy: "Want to dirty straddle?"
Girl: "Hell yeah!"