The origins of the term come from a discussion surrounding a recent case in ireland in which a man blocked his ex-wife's attempts to have eggs which he had fertilized implanted in order to bear children. His arguement was that half the genetic material was his. However, unless said material was taken by force, he must have willingly donated it, there by creating a 'gift' of his sperm. So it had to be true - he'd been spunkjacked, and finally he would have spunk justice.
Interestingly there is no antonym since you can't put it back in once it's out. To date, I am unaware of any cases in which anyone has tried to force one mans semen into anothers Japs eye but if it happens to you then please accept my sincere condolences.
Contrary to popular belief, Spunkjacking is not a victimless crime. At least 2 million of the little white soldiers stand to die in a failed hit. And most men do not appreciate getting a hand job if you don't wake them up when it's happening.
Luckily, you can help cut down on Spunkjacking in your area. When a woman gives you a mouth-based treat, make sure you donkey punch her so she is forced to swallow. Also, having a spare condom or even an empty crisp packet handy can be a life saver.
But officer, I've never even seen this woman before. How could my semen be all over her face, hands and clothing? Dear God! I've been Spunkjacked!