When you are having vaginal sex with a woman and you are about to ejaculate but you surprisingly stick a salmon from the Yukon territories in her anus as soon as you cum.
The act of getting head and right when you are blowing your load you hit the unsuspecting female in the back of the head, and subsequently your jizz will come out of her nose.
Justin is getting head from Magda the cafiteria lady and he hits her so hard he gives her a whitehorse.