When I was a teen in 1982, I read Karate magazine and one issue had a self-defense section for women: in particular for rape prevention. They had one recommendation, of many, that if all else fails... reach down between your rapists legs and make like you are enjoying this horrible event and then grab a hold of the testicles and pull and squeeze as hard as possible.

Being a male, this quote has stuck with me since then: "the testicles pop easily: they have the consistency of a ripe plum."

Is this true and is this a valid self-defense?

There seem to be plenty of quotes similar in nature floating around the web but I see nothing official.