A "Chocolate Wheelbarrow" is when two people are having sex in a wheelbarrow position. The female will projectile shit upon the male's face. The man in a fit of rage (and horniness) will continue and push her face into the bed so it causes her head to lift up and down in the motion of the wheel.
N-word Jim: Oh no you didn't bitch i'm about to chocolate wheelbarrow your ass.
Girl: N-word Jim, please chocolate wheelbarrow my ass all night long.