And Er, Judah's firstborn, was wicked in the sight of the LORD; and the LORD slew him.
 And Judah said unto Onan, Go in unto thy brother's wife, and marry her, and raise up seed to thy brother.
 And Onan knew that the seed should not be his; and it came to pass, when he went in unto his brother's wife, that he spilled it on the ground, lest that he should give seed to his brother.
 And the thing which he did displeased the LORD: wherefore he slew him also.
So it is quite clear that Onan penetrated his sister-in-law (that’s what “went in unto” means), but did not finish the job, preferring the time-honoured but rather ineffectual contraceptive technique of withdrawal, or “getting off at Redfern”, as we call it in Australia.
The Vadney is one of those self-professed Christians who apparently haven’t read or can’t understand the passge, and use “onanism” as a fancy word for masturbation. I love the way he censors the latter word but not the former. Nothing like consistency, is there?
And generations of depraved clergy have deliberately misinterpreted this passage to frighten the shit out of pubescent and adolescent boys who dare to masturbate. To make it worse, Catholics even condemn “wet dreams”.
PS: If you haven’t already seen it, check out my main anti-Vadney blog, and find out why I’m trying to stop him!
PPS: If you are not familiar with the Vadney’s blog, you may be wondering why I even mention onanism.... Well, early on, he accused me and my colleague, Scott Horne, of “Purest pedestrian onanism at its foulest” and “Mutual M...” (ellipsis in original). This from the same Vadney who is constantly berating me for vulgarity and obscenity.