An unusual sex act, generally not one for sensation and pleasure, but instead an achievement in the book of man achievements. While doing a girl doggy style, and quite close to finishing, the man removes himself and stands over the girl. While the woman is on her hands and knees and the man is walking over her (legs on either side of her,) the man takes his penis and presses it back between his legs. In a posture much like the Goat (see penis showing game, Waiting, whichever you may,) the man starts cumming on the girls back, the semen being 'dumped' onto her. An additional beeping immitation enhances the experience.
Right before I came, I hopped up and did the goat. When my girlfriend looked over her shoulder, I gave her the dumptruck as opposed to kicking her in the ass for looking; I believe it was a viable substitute.