While masturbating you have a bowl of weed packed next to you. When you are about to cum you stop, hit a bowl of weed and begin to furiously masturbate. You blow your load and then blow out your hit.
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!"