A guy in a porn film that just hops into a scene to drop a load & then jet.
When there's a guy in the background of a porn flick that is beating off in the shadows and his only reason for being there is to enter the main scene & drop his "product" on the girls jaw line. When that's done he vanishes. Sometimes you may ask yourself, "Where did he come from!? And why!? That was a peek-a-boo popshot if I've ever seen one!"